Simulacrum. Lvl7 spell. Extremely long casting time and very expensive. Once you got this, you’re an archmage.
Your problem in this case is the scope of the story. At this stage, you cannot think merely of an encounter by itself. How you get to the encounter is the whole game. And you cannot be passive either.
You are mistaken on one point: the dm doesn’t deal with a player, a vilain deals with a character. That’s a significant difference.
Which goes back to the archmage bit: if a pc is an archmage, a vilain can’t ignore it. It’s like Sauron can’t ignore Gandalf. The story becomes about the vilain versus the players’ characters. Exactly like in any comics where it more often goes into tier3 than the classic fantasy.
As for the fighters, there is one discrepancy in dnd 5e between martials and spellcasters : spellcasters are given their tools in their class progression while martials need to seek their strategic power into the game.
But this is unfairly putting things actually : a wizard needs a lot of things in the game too. Like the materials for your simulacrum. This means that spellcasters merely have more guidance on what they should seek in the world than martials. Martials players should merely look at the downtime activities to know what they can look for.
Sure, you can add an enemy to counter the martial, but what will you do against the army he recruited?
That is what tier3 is about. That is what 5e rules do to the game. You may not like that. Then pf2e is certainly better for your table as far as I understand.
The problem with 5e is that people don’t understand what tier3 and 4 are about.
If you want to see what tier3 is about, you should have a loot at what kind of humanoid are still in this tier in the monster manual.