Mass assault vs superior firepower

[Achab]

The supply discount under the Deep Battle is there to encourage mass usage of the Katyushas.

 

[Vohen]

One aspect I think might be overlooked on MA is the repercussions that putting 40% (edit: 40? I meant 20%, what an idiot I am) more inf for the same width in your divisions could have besides stacking a higher defense stat.
That also inflates heavily the HP of your divisions, meaning that, replacing the mot for inf on tank divisions, it will not only get much cheaper, but less tanks and other costly weaponry will be lost in combat as well (without having to rely on maintenance companies, so resources saved there), which leads to more tank divisions deployed overall.
If you do have enough MP, your human wave might very well be able to turn into a tank wave on the offensive, and coupled with the supply reduction, you can get to concentrate your forces and deliver a truly deadly blow.
The drawback I see is in relation to the planning bonus there, as you're not really encouraged to rely too much on it (your divisions will have more org and be much slower, encouraging a more protracted offensive).
Now, disclaimer, I haven't tested this out yet, just checking numbers and being experimental here.

The supply discount under the Deep Battle is there to encourage mass usage of the Katyushas.

Is it?
I'd genuinely like to know how, because I always struggle to find a good use for MRART at all.
I feel like they'd only be worth it if they were about 60-75% of their current cost.

In general, SF is a high-quality, low-quantity doctrine. Deep battle allows you to use less supply so it is a high-quantity doctrine. The issue with deep battle is that you can't really make use of the supply advantage unless you are either using low-quality divisions or doing a no-air build, both of these options have weaknesses. Especially with the nerf to NKVD, low-quality nature of deep battle can be a significant weakness due to reinforce problems. I usually prefer mass mobilization for Soviets as the safer choice with very high reinforce and recovery rate. SF and MW are also viable doctrines for Soviet if you want to play a tank-focused Soviet. SF is the riskier choice due to low org, low reinforce rate and low recovery rate but it has more punch per cost.

The almost 20% reinforce rate you get with MA (plus radio researched, not even needing to put signal companies in, resources saved again) are already plenty powerful.
They won't join combat exactly when you put them in, but a 5h mtth is already quite great, even more so when considered the IC other doctrine users have to put on support equipment to get what you get for free.
And I always felt like the old NKVD bonus was quite ridiculous anyway.

But really, the Soviets and Americans can do very well with any doctrine, they have the industry, manpower and resources to do so (the US suffers with it in the early game, but they can escalate quite fast, especially if they don't stay democratic).
Even on GBP, although I feel like that one is especially tailored to benefit smaller nations with an issue both in MP and IC, but because of that it is a doctrine that anyone can use, its perks are pretty generic and don't require a particular aspect of any nation.
(seriously though, GBP is a very underrated doctrine imo, it is my favorite doctrine for minors, it's impressive the punch smaller divisions can pack with those planning bonuses, while also being able to turtle up nicely with entrenchment bonuses, getting you more effectiveness per their very limited resources, with the main drawback being that it puts you behind a pretty strict time table).