@ArisatoMinato American done it to victimise themselves so they can play into the audience with their David vs Goliath mentality.
If the German did it, it would be like a jobless, low life with no education, leeching off his parents write a webnovel where he's the smartest guy in college, have chicks fighting over him and knocking his bullies teeth out. I hope I didn't offend the majority of webnovel author there.
To clear thing up, the manga doesn't seem to be revisionist. It's just a doujinshi artist and a tank crew goofing around being weird young men. There are some usual time travel tropes, but no sign of turning tides in favour of Japan to thwart the Soviets.