Why is this specific mechanic during Relics Quests still that way?

[Elecrom]

Think about every turn-in you've ever done. The reward goes into your inventory. If the weapon is in your main-hand and you turn it in, what job are you afterwards? You have no weapon. No job. That isn't a "state" that FFXIV knows how to handle. Should it be possible? Sure. I wouldn't be surprised if they are wary about making changes to code that has been in place since at least 2013, if not carry over from 1.0.

I know this. But wouldn't it be easier to just let you finish the quest as another class then? The weapon is locked in anyway so there should be no way it could cause problems that way.