FPS issues with minion build

I just died in very juicy map because my FPS just tanked like crazy.
I had barely single digits.
Wasted 40 minutes killing 1 pack at a time at 10 fps.

My mistake was to go to do Savannah and idk why but this map is so bad when you have LOADS of packs of mobs + minions running around.

I swapped from arsonist build on my witch to skeletal snipers because I did read that there is something about how fire renders in the game that isn't quite right. It got better in some maps (factory, crypt, similar areas).

My rig is oldish (2018) and I almost wanted to upgrade it but sadly also I did read that spending 500€ on new gear doesn't necessarily fix the issue.

I made alt sorceress stormweaver and guess what, I got no lag at all. All maps running smooth 70+ fps.

It makes me sad and mad because I really enjoy witch.