Play it as Greece, the fighter CAS with rocket lacks the lovely ground damange punch. From my calculation, a 1940 fighter-CAS in Battlefield doctrine (+65% CAS mission efficiency) can have a module with -15 or -20 agility and still have agility comparable with enemy 1944 fighter . So l can finalize the design of fighter CAS here, just one module to reduce agility: the anti tank cannon.
This misses a couple of important points, and your design is honestly not good at all if you're looking for a plane that can bomb ground troops well and still be good at air combat(spoiler, no such design exists). If your main goal is to maximize damage dealt to ground troops you're never going to be able to get a plane that is competent in air combat simply because every module that you spend on CAS weapons means one fewer module that you get to allocate to air combat. Since you literally can't have a single plane that is good at both, it's best to just pick one and focus completely on it. In other words, just build a regular CAS plane with full CAS weapons instead of a mostly-CAS plane with a single module of 4x HMGs.
And if you really wanted to make the plane you designed better at air combat without really changing the design you would put the bombs or AT cannon in the first slot to make it a CAS plane to benefit from battlefield support's CAS agility modifier. If you're going battlefield support for the mission efficiency you're not getting 10% fighter agility from doctrine - so you should make sure to get the 20% CAS agility by making it count as a CAS plane.
The design you posted would be decent (though not optimal) for bombing ground troops, but the only reason to make a design compromise like that in the first place is to have it be good at air combat too. But here's why that design will be terrible at air combat:
In your post you mostly talk about agility, going into some math on how your mostly CAS plane can keep up with 1944 fighters on agility. You seem to think that having good agility by itself will make the planes able to perform well in air combat. But that is simply not the case. Agility for its own sake isn't very important anymore now that there is a large variance in what each air frame is capable of. Agility acts as effectively a stat multiplier for damage taken, but it's the total damage values that are the important parts of the formula. If your agility is the same as the planes you're fighting then neither side has an agility advantage and the agility does nothing. What air combat boils down to then(as it always has really) is your air attack and defense vs the enemy's air attack and defense.
Before the air rework, there were really only "1940 fighters" etc and they all had the same attack and defense by default. Increasing attack reduced agility for only a moderate gain in attack but increasing agility had no drawback. This combined with defensive modifiers mathematically being superior to offensive modifiers means that increasing agility first was the best way to ensure you get favorable air trades. Increasing weapons was helpful, but only after maxing out agility.
This long history of "upgrade agility first, agility is the most important plane upgrade" being the main commonly spoken advice has led to a misconception that agility itself is the single most important stat that a plane can have - and it's simply wrong.
Now, however, the base air frame provides no attack and only a small amount of defense. You can increase the attack and defense of your planes so much more by adding modules that the agility multiplier really is not very impactful compared to just having much higher base attack and defense.
In your post you see a plane with 54 agility (that would be boosted to about 89 while on close air support given 165% air support mission efficiency). I see a plane with 12 base air attack and 21 air defense(not shown in your screenshot but it would go up to 25 defense while on a CAS mission thanks to the dive brakes), that would be boosted to 19.8/41.25 by CAS efficiency modifiers. Compare that to a standard 1940 fighter with strategic destruction doctrine and light air designer:
With 120% air superiority mission efficiency, the stats of a standard 1940 fighter go up to 76.8 agility, 62 air attack, and 25.2 air defense.
The mostly-cas plane will have a 15% agility advantage, a 63% air defense advantage, and a negligible speed advantage. But those defensive modifiers are nowhere near strong enough to compete with the 62-19.8 advantage in air attack owned by the dedicated 1940 fighter. The standard fighter has over three times the air attack of the CAS plane and will shoot them out of the sky like the great turkey shoot.
Your design also only has 810 km of range, which may end up lacking or struggling for mission efficiency in larger regions or when trying to project power. The standard fighter has drop tanks to get up to 1080 range, a 33% advantage. The armor is much better for air combat, but if you can't reach the combat zone it's not providing any stats at all. A standard fighter if it replaced the fuel tanks with a second armor module would drop in range significantly but would be even better at air combat compared to your CAS design. In fact, when building a test with your design it could barely even gain full coverage of Western Germany from the airfield on the Maginot Line, and was unable to get full coverage from any airfield further away. Meanwhile a design with drop tanks doesn't have to worry about efficiency penalties like that. Compare the smaller circles (your design) to the one big circle which is my preferred multirole design, which I will go over later:
Or compare to a standard fighter, which can cover the entirety of Northern France from five airfields within Germany and can get near-full coverage from another several:
Since I've said a bunch on this already, I thought I may as well do some testing to prove my point. 6000 v 6000 plus radar for full detection, fully trained. Germany gets standard fighters(pretty much the best fighter design you can make with 1940 tech without sacrificing range), full strategic destruction doctrine, light air designer, no air spirits (since none help air superiority when mission efficiency is already at 100%). France gets the Cavalry Multirole design, full battlefield support doctrine, and the continuous strike air spirit.
After a month of combat, the Cavalry multirole design lost 1462 planes, and the standard fighter design lost only 666 planes. Unfortunately I lost the in-game screenshot by letting the game play on so you'll have to do with a slightly less accurate screenshot of the past 12 month losses instead of the last 30 days. Doing the cost analysis on the planes, France lost 1.991 times more IC worth of planes than the Germans did, making the Cavalry Multirole design only about half as good as a normal fighter - not something that should be relied upon if the air war is anywhere near parity in numbers.
Now let's try my favorite multirole plane design - I lovingly call it the "Cas-Fighter Cheese" design. It benefits from +20% CAS agility by having rocket rails in the 1 slot, replacing a 4x HMG module that would be on a standard fighter. It also swaps out an armor module for dive brakes, which saves some range and cost but provides the same air defense while on CAS missions. Otherwise the design is the same as a fighter, with 4x cannon Is, drop tanks, and self-sealing fuel tanks. With the 165% air support mission efficiency, this plane will have 34.65 defense, 104.94 agility, and 66 air attack in combat. That's slightly more attack, way more defense, and way more agility compared to a standard fighter - at least when on CAS missions. On any other mission it is quite a bit weaker, so only use these in their intended role if possible.
Let's see how they perform in combat. Fair warning, I forgot to save the game before the first test which is why I lost my screenshots and to save time training another 6000 planes, I just carried on. So the Germans have a very slight experience advantage and several flying aces to begin this combat, which should in theory give them an advantage.
Any advantage the standard fighters got from mistakes made while testing is still heavily outweighed by how much better the cas-fighter cheese design is when used for air support. They may have only done 170 bombing compared to the 751 of the cavalry design, but they completely shredded the enemy fighters. 1613 cheese planes were lost, but they shot down 2476 standard fighters. Doing cost-efficiency math shows that the cheese plane is 61% more cost-efficient in air combat compared to the standard fighter - and that's including testing errors that favor the standard fighters.
That's why I call it a cheese design - It's
over 60% better than the best possible fighter in air combat. This is almost certainly a design oversight, and it doesn't make logical sense either - a plane only partially dedicated to air combat should not be better at air combat than dedicated fighters of the same tech level - but it is. Exploit it as much as you want.
You don't build them primarily for bombing ground troops, but for destroying enemy fighters. The bombing that it does do is a nice side benefit. Once the enemy fighters are taken care of you can send in dedicated CAS planes to mop up the enemy ground forces. You can continue using your cheese planes for the small amounts of bombing that they do provide, or can even convert some of your cheese planes into full CAS planes once you've won the air war to rapidly expand your CAS forces, since you won't need as many fighters anymore.
End Essay.
