With limited MP pool and only a margin of our spells even being useful, I don't think having access to all spells at once would be overpowered while we only gain traits from those set, that sounds like a perfect idea because Job Traits are the only main reason it'd really even be overpowered. And if your worried about because we'd no longer have to set damage spells to take up our points, then lower the number of points o something to allow fewer traits.