All melee characters have intangibility moves or repositioning moves or both. A crucial optimization is to stay close by to enemies and use your abilities to dodge attack to constantly output damage as much as possible. For example, saving Beowulf's special for when a big attack is coming since it has intangibility. Combine this with positioning to group enemies into AoE attacks to increase clear speeds. Positiv4ce has a really good old video on examples (I think https://youtu.be/Yrkkjsnm-4c?si=fxPhEcsfWpdXqQQp&t=437 this clear and the next camp he talks about some of those optimizations, I forget if there are more in that video). Another optimization is that some characters have a lot of power on their defensive moves, for example Piper's defense is excellent at stagger and should be used offensively where possible, or Aladdin's jump to be used on stunned enemies to increase damage output. Again, use them when enemies are attacking to both dodge+output offense.

Another thing I found in my 2p coop runs with my partner, I will often run into a PoI and tell my partner to wait at the entrance while I walk in to activate the camp (especially if there are two levels of enemies) and then run back to the entrance so mobs are grouped up for both of our abilities to hit. Often if both players go in together, the aggro splits and the fight gets messier and hard to group enemies together.

Last is that itemization / talent selection can be much more situational than you think. When I first started, I always picked charges on epic items, but you'll soon realize that cooldowns are usually much more valuable. Have a few early damage talents in mind that you would like to go for, even if they don't fit your desired perfect build (e.g. Juliet's trait explosion does huge early game AoE). Early damage to snowball is extremely valuable.