Right, I agree with what you're both saying here. My long example was showing the design challenge of how to take just one small thing that has come up repeatedly – high level mundane fighters should be able to jump higher – and illustrate the problems with tackling it in the way 5e handles jumping rules with hard numbers.
You can break away from any real life references, I get that, but then it's a question of degree – 30 feet high jumps? Are you the player still feeling grounded in the mundane fighter fantasy of "what a person can achieve with skill, wits, and blade alone"? 50 foot high jumps? 100 foot high jumps? Where is your line? Hard number design demands we establish an answer and some kind of reason for that answer.
Or you go in the direction
@Oofta is describing, more narrative a la "Athletics checks to exceed jump distances", but then the rules are silent and you're getting closer to narrative mechanics waters. And inevitably that's going to start losing some 5e players as it's bucking the microtransactional trend of 5e's class/character design. Narrative mechanics design demands we consider both player tolerance (how far in a narrative non-numerical direction can we push this?) AND how the proposed rule plays with existing rules (or the lack thereof).
Basically, I'm using high jump as a microcosm of the big picture design challenge with a mundane high-level fighter. You can apply this line of questioning to almost any proposed change to the class, looking at tension between hard numbers vs. narrative design, whether the design change preserves the "mundane/grounded" fantasy or stretches it too much, whether the change is interesting/meaningful or too microscopic/microtransactional, etc.