I like the idea of a fallen paladin reverting to a fighter - and I'm sure this is more or less what happened in 3e? Your lost your divine powers. An anti-paladin/blackguard was something quite different - either by origin (choice) or as a consequence of some terribly evil act when a paladin.
I think if you 'fall' as a paladin you shouldn't just pay a GP amount to get back on track. There should be some sort of short quest to recover your status - and a flag set so that if you do it again, you can't atone a second time. That said oathbreaker is way to easy to trigger in BG3 (often unknowingly) ...
I played a paladin on my initial run and was always worried about smacking the wrong thing lest I break my oath. In tabletop, I played the same paladin and that was never an issue...bad guys were bad guys, end of story. All these moral quandries about smiting a goblin (because they didn't attack you first - even though it was clear they were about to etc).
