I don't know why you would think I want to restrict the mechanics. I don't have any particular issue with giving Fighters spell slots and letting them cast martial 'spells'. Use whatever mechanics you like.
But the issue is this. If you have a Fighter spell that has the same mechanical effect as Misty Step, then it is only really not a teleport if you are going to stop it being used in circumstances in which there is no other explanation of the spell other than 'teleport'. You could let it happen anyway and not care about what happens in the fiction I guess, but if you do care, then the fiction imposes constraints.
The issue here is fundamentally conceptual not mechanically. As long as Fighters are constrained by basic ideas of what is real and wizards get increasingly wilder and more earth shattering ways to break the laws of physics, there is a widening conceptual gap. That means that you can only really balance them, to the extent that 5e does, in the realm of the thoroughly abstracted such as damage.
It doesn't matter what mechanics you write. Conan cannot conceptually be balanced against Dr Strange. If you want to balance a warrior against Doctor Strange, then at the very least you need Thor or the Hulk.
Sorry, wasn't calling you out. Just adding to the thoughts in your post which seemed to be going in the same direction.
Seems like we are very much on the same page.
One way to balance against Dr. Strange = Hulk (mythic martial)
Some people want a Black Widow (action hero martial) to be able to adventure alongside Dr. Strange and have the same importance/impact to the story though. I have no problem with this.
This is impossible using Black Widow's on paper power set though.
AND on top of this, it is difficult to model even this level of power -- typical action hero stuff because of current mechancial limitations that some people are demanding on martial abilities. (will saves have to mean mind control, etc)
One way to do this is with powerful limited use abililities. Another way to the power of mundanes is to do this is by abtraction or meta currency.
For instance -- even though Black Widow can't fly, circumstances often make it so she can use her skill set to accomplish the same thing in a combat scene. She parkours, jumps off platforms, bounces off other huge enemies, and makes it to a building rooftop 3 building over. Thor flies over and Hulk jumps in one jump.
But from an rpg point of view, the
player needs some mechanic to trigger that all those things are available. The dragon lowers its head at just the right time for the mundane to jump on it and off again onto the high ledge with a cave opening.
This maybe can also be done with limited use abilities that follow traditional action economy (maybe), but seems like there is a lot of push back there as well because if you use existing mechanical contructs to do this (will saves, always works, etc.) then you get this "turning things into spells" deal even if the fictional representation is purely mundane/action hero.
I just had the realization of the extent of this mechanical hand tying going on. I always thought it was mostly a conceptual issue, but people are having trouble "giving nice things" to these action heros even after agreeing that this is the concept.
From your other posts, I don't think you disagree?