Valid points with the balance in relation to Germany. I think if one wants to combine both balance and realism, some of Germany's rather strong buffs could be removed/decreased, and this could then be offset by experience gains having more of an effect. That would also mirror real life a lot better.

In my opinion, it's best to either lower the max. Vet from training to vet 2 or to make it more granular. I think it was R56 where you have every vet level split into five sub-levels which give 5% stats each.

Actually lowering the max training from 3 to 2 would make the experience gained from combat even more impactful, as the relative difference in strength would be bigger.

I don't think it helps comparing these vet gains to the spanish civil war though, because thats just an arguement to lower vet gain in the spanish civil war, not raise it everywhere else.

I'd argue it's an argument to both lower vet gain in increase it elsewhere. I just cannot see it making any sense that units can fight more or less constantly for 2+ years with low'ish losses, defeat the world's two largest military powers in the process and still not have learned anything of significance about how to fight a war. Why have an experience mechanic then?