do u see rifleman getting wiped by explosive as much as gren ? last time i checked 5 > 4, be 20% less damage or 1 more man it does not really matter
saying green should be the only main line weak to explosive If it isnt bias then i dont know what is. 
I see riflemen getting wiped by bundle nades quite often in high rank games, especially after last pgrens buffs. I also see all infantry squads getting wiped by stuka zu fus every tournament, apparently not a problem.
Saying ostheer should have some weakness (even if only its infantry) is not a bias. What about 5 men upgrade for grens? 5 men with 20% reduciton, how is that balanced? It will be new meta defense (it already kinda is).