I would just half the bonuses from ability scores and double bonuses for proficiency.

So like say a 5th level char with 16 strength, would get a +7 to attack rolls, +1 from strength, +6 from prof.
It solves this probem real quick of classes working but not needing ability score to ride.
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I like powerful build and heavy weapon thinking, a small sized creature can still be very athletic, which is the prime concern of the strength score, so good at climbing, swimming, fighting, etc. But that doesn't have to translate to dead lift. I saw a homebrew version of kobold that traded the -2 strength for slim build (strength halved for carrying capacity), I much prefer that way of thinking, as str in dead lift terms doesn’t usually mean much in combat.