Well, the main issue there is indirect fire. Indirect fire/long range weapons arent an issue in other games because you just blob up to them and take them out. But HMGs/suppression are meant to discourage blobbing and give the defender an advantage, so they facilitate indirect fire to an extreme degree. Just imagine if any of the games where indirect was 100% accurate had suppression. Even if that problem were ironed out and indirect fire projectiles landed where the unit used to be and didnt track targets, then countering indirect fire just becomes as simple as moving your unit. This means that hmgs and team weapons get screwed over because they can't move at will, and it becomes all core infantry...which is essentially how all other RTS games play...
Overall, my point is that basically every interesting mechanic that coh2 has is entangled with the existence of rng.
You are right. Coh and DoW franchises are pretty much a whole new generation of RTS genre and that is mainly due to introduction and clever usage of rng.
Btw, I wonder how they will solve the question of rng usage in AoE4. Are we going to see typical catapults/guns firing into old position of the troops, or are they going to make it a little more immersive with a pinch of rng?