This post it about making the Quarks more fun to fight against but as well as make them more of a threat. The current AI for them has made them easy but very annoying to kill as most of them are just bullet sponges which is not enjoyable, its fine for the grunts but the elites as they are very tanky on the later missions.
With the upcoming Primal Quarks, I do hope they are not just more bullet sponges with increased attack damage as thats not fun to fight against, not to mention easy.
One idea is to remove the part of the AI which makes Quarks circle around you which should make them more aggressive and chase you down more effectively as right now you can dodge them pretty easily. This should be primarily done on the swarmer Quarks like the Wolf, Leaper and Sprinter as to make them more of a threat. This part of the AI should remain on the smarter Quarks that would try to outsmart you and be tactical, namely the Cyclops, Bulwark and Whiplash.
Alternatively you could increase the rate they are to attack to make them more of a threat once they get into range of you, that is of course if they can since you can still kite them forever.
Another idea would be to add a attack for the melee Quarks that enables them to hit you when flying as you are essentially invincible in the air since most Quarks cant even hit you and the ones that can are usually in small numbers and not that effective. A sort of jumping/leaping attack may work which could disrupt your flight and bring you to the ground.
A idea discussed was to actually remove the Crystals invicibilty buff and replace it with a speed or damage buff as to make the Quarks much more threatening when in its effected radius. Right now it just makes it seem like a time waster since you can dodge Quarks pretty easily and most cant even get into range to hit you effectively if they were to even try attack you in the first place since they just circle around you.
That or replace them with the Guardian Quark as to make the level containing the Crystals more dyanamic and fun.
While that last comment of yours was less about the AI, I think more crystal types, as well as a more visible area of effect for them, would be nice.