Yaarel
🇮🇱 🇺🇦 He-Mage
Not a fan of your idea for tying Dexterity to Athletics. Seems like you're exacerbating the dominance of that ability with that houserule.
Dexterity requires a serious redesign in order for the abilities to be equally useful. Until that happens, giving a minor perk like Athletics to Dexterity is negligible.
Athleticism and balance are inseparable aspects of gross motor skills. Splitting them up is wrong and ignorant.
Mechanically, the dislocation harms the game by crippling the agility tropes within the fantasy genera, by forcing multiple-ability-dependency to invest in both of the redundant Strength and Dexterity.
The current situation of agility is a perpetuating pain point. I want to see this resolved, at almost any cost.
There good reasons to give Athletics-Acrobatics to Strength, because D&D Strength is agile, wielding swords accurately, wrestling, and so on. There are also good reasons to give Athletics-Acrobatics to Dexterity, because one cannot Climb without Balance, nor Jump without Falling. Tumbling (somersault) requires significantly powerful high jumps. So on.
Ideally, Athletics becomes its own ability, distinct from both Strength and Dexterity. But between the two, Dexterity gains all Athletics, on balance. Strength strongly correlates Constitution and its Fortitude save, especially for brute tropes, where Strength and Constitution function as if synonymous. This leaves Dexterity with its Reflex save the best match for agile Athletics.
Reflex requires gross motor skills, sometimes jumping out of the way of an explosion, boulder, or whatever physical danger. Reflex = Athletics. Whichever ability gains Athletics necessarily gains the concept of Reflex saves and the skirmishing AC dodging and blocking bonus. Ultimately, it is Dexterity − specifically the aspect Balance and Reflex and AC bonus − that merits Athletics most.