Those people who skip to the end and get combos for Srank and whatever do not do that in Dragonica. You will be slowing the run since 90% of the time it's a non-AoE class preforming this trick, and it's cute below 30 but just wasting time afterward. You are of more help trying to get a few combo points on small groups and preforming a duty for your party than trying to beat the system.
Though it usually works best that way, the cleaners don't absolutely need to split up, they can stay around the other cleaner if they sync well. This should usually be a judgment based on the form of attack, ground based or aerial, but it can be also dependent on skills. For example, Aco can't attack things in the air or fallen down, so you would avoid using skills that do either around them. Or Gladiator and Trapper have plenty of skills that knock enemies in the air, both of whom can abuse the air bound enemies with some air combos.
Although Jesters and Battle Mages serve an important role in this game for killing groups, the other classes need their rep for killing those smaller groups with the same speed. Get out there and level with no AoE whoring or class discrimination, and the world will be fine, but also understand: When a party has 2 filler classes and an AoE present, they aren't kicking you cause they hate your class, they're kicking you since that's how it works.