Ovinomancer
No flips for you!
Here's my issue with your suggestion: it creates a strange narrative place where the 24 STR Barbarian not trained in athletics and who didn't put his points there wonders why he loses at arm-wrestling to the 4 STR (rolled, of course) Wizard who is trained in athletics and spent his points there. By decoupling, you've created a system that requires the expenditure of points on the physical skills to replicate the effects of stats. Failing to do so creates situations that don't make sense in the fiction (very strong people unable to effectively compete at strength related tasks with very weak people). This means that the physically gifted character archetypes have mandatory spending in your system.
I agree your system addresses some of the wonkiness with mental skills -- where some people are just good at skill group without generally high intelligence, but those kinds of outliers might be better served by a feat rather than a rewrite of the skill system.
Something like:
Feat: Savant
When you take this feat, choose a skill.
1) You gain expertise with this skill.
2). You may replace the associated stat bonus for this skill with a flat +3.
You may take this feat multiple times, but must choose a different skill each time.
SPECIAL: you may take this feat at character creation, even if you do not qualify to take a feat. In this case, you only gain the second benefit of this feat.
I agree your system addresses some of the wonkiness with mental skills -- where some people are just good at skill group without generally high intelligence, but those kinds of outliers might be better served by a feat rather than a rewrite of the skill system.
Something like:
Feat: Savant
When you take this feat, choose a skill.
1) You gain expertise with this skill.
2). You may replace the associated stat bonus for this skill with a flat +3.
You may take this feat multiple times, but must choose a different skill each time.
SPECIAL: you may take this feat at character creation, even if you do not qualify to take a feat. In this case, you only gain the second benefit of this feat.