One day, I hope to actually play DnD.
I understand where you’re coming from but there are a ton of ways you could spin it so that it would still make sense to me, like maybe ‘the process of the oath itself is a little bit divine’ or ‘the gods are the ones providing your magic, it’s just mostly in the form of arcane/primal/whatever powers rather than divine’For me... it's a pretty great idea and I already do it to various degrees.
The -rest- of the class often makes it stumble. You used the Paladin as an example so Lay on Hands. Arcane casters (other than Bards who, really, should be considered Occult in my opinion) don't get healing magic, but one of the most basic features of the Paladin is a healing effect. Divine Health. Sacred Oath. Cleansing Touch.
The class is built from the ground up to fulfill a specific "Fighting Priest" identity for D&D that doesn't quite fit in with, say, a Spellblade.
Which is why 5e throws arcane spellcasting at the Fighter and Rogue who don't have those particular impediments. Heck, even the Arcane Archer isn't offered up to the Ranger, arguably the closest thing to an "Archer Class" as 5e has, but instead gets sent to the Fighter.
And that design is even stronger in A5e, where class identity gets cranked up even harder with their social and exploration abilities.
It requires a lot of refluffing and a little suspension of mechanics, more than some players are willing to go along with.
Just boiling down to: no matter whatever source a paladin ends up getting their power from, those abilities are fundamental to being a paladin, and thus will still manifest regardless, I recognise this might not be a satisfying answer for some people but I don’t have a perfect solution.