which brings me back to the copypasta I put in the OP - since spellcasters and fighters can't deal with the same challenges at the same level, you have to either cater to one or the other.
If's it is hard enough to challenge spellcasters, the fighter is going to suffer
If it's easy enough that fighters can handle it, spellcasters will either blow through it or you will have to gimp them with shit like anti magic fields or steal their spellbooks or something gimmicky like that.