I know this is affected by the dumb leveling gimmick where being a higher level than enemies gives you reduced exp, and that is also a mechanic that should be done away with; Nobody liked it in pso2 base, everyone was happy when it was removed, and it's equally as annoying here. But that's a topic for a different day.
I'm embarrassed to say it took me til lv 18 on my 5th class to notice, but bosses need to give more exp. I was grinding resol forest, killed random spawn nex, and saw that the exp it gave me was in the low 1000s (didn't see exactly) so I started comparing some of the enemies.
Pettax gun gives 447 exp
Elemental lizard gives 149 exp
Pettas sword gives 286 exp
Silver Nex aelio and silver daityl axe only give 1789.
It's absolutely insane how using a few well placed AoE attacks in a group of weak enemies gives more exp than playing out a whole boss battle. And just to clarify; I'm not asking to nerf the exp given by small enemies, the grind is frankly a bit much in the sense that we're technically in the early game.