It is useful but it is not broken as some people described it. In 1vs1 2vs2 modes 2 PzIV are simply better than 1 PzIV and C. PzIV. They trade lower price and better gun for 1 extra hit in normal PzIV.
C. PzIV is problematic mostly because it available with Puma for not tech cost.
What you say might be true for 1v1, but its utter bs for 2s.
CP4 makes a massive difference when you're making a push or defending against one as it massively increases survivability of both armies near it.
The effect may be only 10%, but it snowballs with the number of units.
There is a difference if you are fighting against 1-2 units with 10-25% more effective hp and if you are fighting against 2 whole armies with 10-25% increased EHP and its best EHP increase in the whole game since its non RNG modifier, unlike armor or rec acc(its 25% EHP increase for P4s for example despite the bonus being "only" 10% in value as you need 1 additional shot, its 10% hp increase pretty much only when infantry is fighting rifles who do 8 dmg and penals who deal 10).