The reality is that "schwerepunkt" tactics assume that the enemy is mainly going to shoot its AT weapons at the big, scary heavy or medium tank up front that's bearing down on them, not the host of little ones in the back that are just waiting their turn until the enemy has revealed its AT gun positions by firing.
As stated, you don't use light tanks against enemy tanks, but if the enemy tries to put infantry in the way of your advance, the light tanks are fast enough to avoid combat and continue on to the objective, or more than sufficiently powerful to break them if they do get in the way, while the heavier tanks either crush anything that the lights leave behind, or deal with enemy armor.
Late war, the increased presence of portable AT weapons made light armor less relevant, and it didn't make much sense to continue building it instead of ramping up medium tank production. Since it was already built, it was still far more effective than not having armor around when and where you needed it. Being vulnerable to AT weapons while in a tank can't have been a lot worse than being vulnerable to every rifle, machinegun, and mortar round while slogging along with nothing more than a canvas jacket for protection.
I'm reminded of an order given to Hungarian tankers in their Italian-made Ansaldo tankettes (bought for training purposes, not combat) at the start of Barbarossa, because the domestically built Toldi light and Turan medium tanks weren't available in sufficient quantity to equip more than a division. "If Soviet tanks are spotted, bail and run." The tankettes had nothing that could hurt a Soviet tank, were too slow to run away, and had barely enough armor to stop a rifle round at medium range, much less a main tank gun round. The crews were far more valuable than the tankettes, but having a mobile machinegun emplacement to deal with enemy infantry entrenchments was a lot better than having infantry run headlong toward enemy machineguns.
In HOI3, you could upgrade armor from light to medium for significantly less cost than building new armor from scratch. In HOI4, where you build "equipment", you will likely end up with some leftover obsolete tanks from your tank divisions. It makes perfect sense to use them in other roles.
There are probably several names for the kind of warfare that doesn't use anything but the best: "brute force", "overbearing", "ham-fisted", etc. Try running an industrialized minor country and see how much you can do with a LOT less. That forces you to learn what can be done with the units you have, not what you wish you had. Can you go toe-to-toe with the Soviets on a narrow front during Barbarossa, and hold your own, or even advance? Can you stall the Germans as Belgium until the French reinforce your lines, and force a trench war instead of Blitzkrieg?
BTW - running Germany without a navy means that Italy and Japan will face the brunt of the combined UK and French fleets at the start of hostilities, and likely suffer badly. In HOI3 Germany games where I built a modest but effective Kriegsmarine, Italy and Japan went ballistic. If I didn't, they essentially got spanked early and did practically nothing all game.
