Keeping the full kit would be stupid and a total disaster in terms of discrepancies. The idea that there is already big discrepancies between player skill, gear, sprouts, etc, isn't an excuse to introduce even more lopsided systems. No matter what you do, no, having Foul/Flare in sastasha is not gonna be healthy for the first time experience of new players that go through here. Stuff already melts way too fast due to SE being extremely bad at keeping powercreep in check from affecting older content, so imagine when instead of your highest potency GCD is not 300 but 900 in there?! (and yes some later jobs like DNC/PCT are the exact example of why this is bad)

The only thing I think could actually work would be to introduce multiple tier segments allowing jobs to keep all of their abilities pertaining to said tiers. For example, a lvl1-30 tier allowing people to have all the job unlock toolkit no matter if in sastasha or in haukke, a lvl31-50 tier allowing to have the full ARR core kit of the job within the lvl31 to 50 duties, and then a tier for each expansion, for example allowing a party in Sohm Al having access to the full HW kit if they have it unlocked.