^ This. Some artistic license is fine within reason, but it's always bugged me when someone suggests something which is completely out of sync with the technology of the time, barring RA1-specific examples and appropriate context. For example, yes the Soviets in RA1 had Hind helicopters (early 1970's tech) and rapidly developed their jet technology (MiG-23) later in the war, but they were also still using Yak planes (1940's tech) at a time when they had already largely switched over to MiG-15 jets in our timeline. Plus a lot of the more advanced technologies were fielded only towards the end of the war (Longbows), and even then many examples were only prototypes (Phase Transport/Tank, Volkov) or very early production versions, and consequently were very rare (Tesla Tanks, Shock Troopers). Basically, RA1 is a case of a few specific areas of technology being more advanced (aircraft, some areas of electronics) while other areas are the same as they were in our 1950's (most common military technologies and the vast majority of civilian technologies) or even slightly behind (A-bombs, initially at least).
As for the Grenadier, I agree with JigglyJie and des1206 in that I think the Grenadier is largely fine as-is and there's no need for any revolutionary changes with this unit. The Grenadier is easy enough to counter if you know how to do it, just like with any other unit. Snipers and Artillery can be particularly effective against a distant Grenadier. Captains, Rangers and Light Tanks also work well.