Jester David
Hero
You problem doesn't line up with my game experience (current level 14). Note: Paladins get their aura bonus to pass concentration checks because they are saving throws. I've whacked the Paladin around *a lot* in game, and the times he has lost concentration have been like 1:10.
Also if casters - full or otherwise - really want to protect themselves against concentration failing, there are two feats that will help them.
Concentration adversely effects NPC spell casters a lot more than PC's, because they usually only do fight one combat per day. They can either focus on staying alive, doing damage, or doing crowd control, but not all three, which makes them ineffective opponents to fight against a lot of the time.
According to the DMG, a level 14 monster should be doing 87-92 damage each round. That's DCs of 43-46. Multiattack does take some of the sting off that, which helps (as does using lots of lower level monsters). But two attacks dealing 44 damage is still two DC 22 Concentration checks. The paladin should still be having *some* troubles, especially since Con isn't one of their saving throws, so they don't get proficiency.
But the paladin should also be doing much better than the poor ranger who also can't take Con saves and doesn't have an aura boosting their saving throws. Poor, poor melee rangers.