the concern here seems to be keeping magic and melee equal.
This shoudl only be a concern when the players are fighting against each other.
Wizards and other spellcasters get nerfed many ways.
Many high levle enemies have spell resistance.
Many extraplanar entities have huge swathes of immunity to the most damaging of types like fire, lightning, acid, poison.
If it is truly a need to 'weaken' magic, I'm just going to go the opposite route and provide some of those common resistances to the warrior types in the game as built up immunity from hanging around all those powerful spellcasters all that time.
There's no doubt a perfectly sensible argument that a spellcaster would just adapt their combat tactics to attack the things their target isn't resistant to. A spellcaster can also do perfectly well for the group without ever casting a single offensively. Buffing, summoned monsters, and 'area denial' magic are all sensible tactics. However, to some extent this misses what I think some people (cetainly me) dislike most about the ubiquity of magic. Past a certain point it solves the part of the game that isn't combat. The chasm has no saving throw against being flown over, the wall doesn't have a save against spider climb, the plane doesn't have magic resistance to plane shift. If the problem is mundane then there will be a mundane skill that can solve it, and there will be a spell that can solve it. If the problem is magical then it's not likely there's a mundane solution. Reduce the spellcasters' toolkit, and mundane skills and clever solutions become much more viable.