I don't want to semi-necro the thread, but it's only been a few weeks and I don't want to make a new one either.
I played a vanilla 1v1 with a friend (relatively casual player but knows how to make templates, micro enough that he's won them before, build industry, etc.) as the USSR, and decided to go with the space marine strat. Since there was no USA/SAF and my friend took the treaty relatively late I didn't get HTD 3 until late 1940, however I had a huge stockpile of HT 2 and both conversion techs so I was able to have around 72 space marines (with just ~30 factories on them) in addition to 12 12/7/2 heavies and some 240 20w normal infantry.
They were insanely OP. He made 14/4s to try and push them but I was able to just bring in my heavies, and since it was in HMM it wasn't like he could force attack to win with them (like Japan sometimes can). He also made some light tanks with LSPG but they lost so much equipment that he ran out of it before he even reached the Stalin LIne. His actual tanks couldn't push through even 2 of them with 2-3 normal infantry while attacking over the river line (albeit without amtracs), and while they did have SPG in them and air support to carry them through the Vitebsk gap, they could only do so on the plains tile and I could easily counterattack. Even with perfect micro, when he clicked my tanks first, I was able to coutnerattack with the space marines and deorg him enough to actually have my tanks defend.
By the time he called it in late 1942 (we played to stalemate, since without a Dday there isn't a ton I can do either) my infantry, which were grouped into a separate theater, had killed 4000 tanks by themselves and only lost 800 HTDs. Naturally a 2 or 3:1 ratio is to be expected for a defensive war - but 5:1, without their losses from my actual tanks, was insane and would be insurmountable for the Axis in a real game.
Next time we play I'm going to have him do the same on Russia and see if I can break it with amrtac SPGs, but I'm doubtful.