It might not be for everybody, but I'm a huge sucker for classes. They really help shape your playstyle and give you something unique I feel.
Each class can get a tweak unique to them and a passive that reshapes how you build completely, giving you some creative build variety.
Wizard class can get a passive like 1 extra spellslot, and can choose ONE between some unique tweaks like these:
Combo caster: Casting a combo spell reduces the cooldown of all spells by 20%
Tempest: Using a spell while in the air reduces gravity by 50% for 3 seconds
Magic Weapon: Every enemy you kill with a spell increases your fire rate by 3% for 5 seconds, capped at 25%
You probably think these could just be tweaks by themselves, there's no point in having a class. And fair enough. But this gives you a reason to have a powerful passive and one free tweak. It's very important that classes don't SPEND resources like tweaks, but give you additional resources that cater to a playstyle. Tweaks are an important resource for making a build, and a lapping these up to "should just be a tweak" does little to create a unique playstyle, which is what classes should accomplish. It's about giving a build an identity.
Imagine a class that gives you 1 extra tweak slot for your character, and a unique tweak like 5% movement speed for each equipped tweak, or giving each unique tweak an extra 5% chance to activate. (so if you have 2 ammo supply tweaks, you go from 10% to 15% chance.)
Or a class made for movement. 1 additional dash, and a tweak that makes it easy to maintain momentum between dashes, or dashing increases reload speed.
I think this game could really benefit from a class system. It would define players playstyles, it would open up new possibilities for builds, and It's really fun to meet people who enjoy a certain class as much as you, and see different builds other players cook up. It also gives way for team composition to shine. I think it's really worth considering.