I've been thinking about this for a long time. I've played a lot of characters who could be members of a given class, if not for the need for a high score in some ability or other. A rogue who story wise is hyper-intelligent, impulsive, and doesn't really understand other people easily, who is MC wizard because his story needs him to have spent most of his adult life ignoring a knack for magic, only to realize he needs it within the last few years (so arcane trickster would have felt wrong), and his high Int means that wizard is the only caster that mechanically works.
There is an incongruity with him that will always bother me. Given his enviroment, his strong faith, the animistic nature of that faith, etc, any of ranger, paladin, druid, or even cleric, would have made more sense. A bard that doesn't rely entirely on charisma, one of his lowish stats, would also work, but I MCd Wizard because it got me ritual casting and spells to counter enemy casters, and it didn't require me to build him with high stats that don't make sense for him.
On the other hand, in my in development game, Quest For Chevar, your ability scores are just a personal resource pool. You spend from Will to salvage crap rolls or activate spells, but you don't add any of the scores to a skill check. Skills are purely about training. You roll your action die and rank dice, and that's it.
So, I've been wondering, could DnD be made to work in a similar manner? Has anyone tried anything like that? Perhaps reducing the number of stats would alleviate these sorts of issues, so your Mind stat covers all the spellcasters, or something?