Under this appproach to the game, how does anything matter?
It doesn't, really. It's a game, after all.
While it's true one character can go invisible and another cannot, the implications of that entirely depend on the DM, even with the full list of what the condition means.
I am now left to wonder if people regularly play or see play where spells are massively nerfed and martial classes RP huge game changing things... and if so I wonder what stops the casters from role-playing as well as those super great RPers that play martial classes?
There's no nerfing required. Spells only do what they say they do, but I haven't seen any spell that compels the DM to allow the consequences beyond that to matter.
For example, let's say you have invisibility. There's a list of things this implies under it's conditions but the DM has all rights to cancel every single one of them. And they can do it sensibly too, without really even considering it.
You turn invisible: You can hide anywhere...but actually these guards have dogs and the DM considers dogs to rely on their nose, so they'll immediately notice your presence anyways within nose-shot. You have advantage on attacks and others have disadvantage on attacks...but this enemy has cleverly kicked dust up and can see you and partially obscure them, granting advantage on their attacks and disadvantage on their own, effectively negating that.
It really would be unfair if the DM does this very often...but it's within their discretion. The only thing the wizard could cast is "get up and leave the table" spell, but it's essentially a suicide spell.
So the perception that a martial cannot, say, jump 120ft off of an ability check without the DM is true, but the same can be said for the wizard that cannot fly to the other side of a chasm because a massive wind gust appeared.
My conclusion is that DM's are just too impermissive for characters not using spellcasting in general. And yes, a somehow equally strengthened wizard might be able to do the same thing as a martial, tied to the ability system, but it doesn't matter because the core question is less "can I do this over other players" and more "Will the DM even allow this?"
Both statements "I jump over the pit" and "I cast fly and fly over the pit" is the same question: "DM, can I use my abilities to bypass this obstacle?" Which the DM can respond with "Yes" or "No." And if the DM replies to the Martial "No." More than the casters specifically because he doesn't like the idea of a martial jumping a fantastical distance, the DM should realize that a magic caster is just as fantastical and the idea of magic being able to do impossible tasks like flying and teleporting is only reasonable because fantasy says that it is. But it's the same fantasy as the martial jumping impossible distances, within the genre.
