For a purely test scenario: create human mirrors of the the all elf/half-elf party and give each one a combat feat related to their specialty. Do a head-to-head fake combat. Assuming darkvision is background noise vs. any properly equipped party of humans (i.e. they have a couple of light sources) it may give a feel to the power of feats. I have a fighter build I have yet to really get to play (spear+shield+polearm master feat) where at level 1 not only is there an extra attack, but the AoO is also awesome. If the equivalent original PC is "sword and board" they get only one attack. If they are 2-weapon fighting, the don't have the shield AC. And when they close to attack, free AoO. Same sort of thing could be demonstrated with synergized feats for most classes I'd think.