[Soapy]

I don't think unwanted traits should stick around until your next LE.

This is mostly referring to things like Arcanic Study (+1 SP to Mage and its promotions), but also the ones that affect growths.

The +1 SP traits and Exceptional Skill don't reset on the basis of "you can spend it and then reset", but there's a very easy solution to that:
If you spend any points given by the trait, that trait doesn't get reset.
This might sound like more work than it's worth, but it's as simple as checking to see if you have 2+ TP remaining, or 1+ SP remaining in each Mage class.

I don't know the reasoning for Talent: Traits, Style Blending and Lady Luck to stick around, but with the new traits being thrown in (and me working on suggesting a few new ones), I think it might be time for that to change. Maybe.

[Neus]

The ones that affect growths can't be unlearned so you can't just get the benefits while leveling up, and then use a reset fruit at max level to get all the benefits with none of the downsides (which would, of course, be this.) So it's very much intentional for this reason.