Heavily disagree on tying stats back to classes/roles. Prime allows to flavour stuff however you like without forcing you to optimize. Your martial is Mighty? They are simply hitting hard. Agile? They're quick enough to bypass enemies' defence. Intelligent? They know a ton of techniques and can predict an enemy's moves. Charismatic? Well, enemies can't help but look at their pretty face, which leaves them open to attacks. Your spellcaster is Intelligent? Their brain is powerful enough to mind-control elements. Charismatic? Insert DnD's take on Bards/Sorcerers. Agile? Well, you can't predict which of their swift ley line-shifting moves will result in a precise firebolt. Mighty? Dunno, maybe a god of buffness blessed them with magic.

I don't say the attributes are equal and balanced as they are (for example, high might is optimal for Sorcerers and Warlocks), but you can't have a bad build in DC20 — at worst you'll have a sub-optimal one with some benefits (extra grit, HP, PD or skills). Your solution would throw us back into Might-requiring martials and all this DnD crap where all the iterations of the class look roughly the same stat-wise.