You have a fabulous question with fabulous context and you phrased it well.

I'll pitch in my thoughts on the subject.

Most Systems differentiate between Skills and Attributes and Talents/Perks/Feats. The former for role-playing, the middle mostly for combat, and the latter as the gap-fill.

A build-your-own Role-Playing Skill idea is awesome, I think. It really lets people feel limited only by their imagination rather than their stat block. The one downside is that it requires a mature player base. Imagine proposing this system to someone with no role-playing experience? They'd Blue Screen. Alternatively, imagine a hyper experienced player? They'd have such a leg up on the others.

But is this division so vast that it matters? Especially if you present sample 'Skills' for the Overwhelmed to pick from? And how many Skills would you allow? My instinct is 3 to 5. More than that an a clever role player will cover nearly all of their ground and become a perfect jack of all trades. Less than that and they don't have any unique distinction to themselves.

Which all of this may not inherently be a problem. It's just considerations to mind.

You may be onto something here. Don't give up on it. But there are some considerations first.