I didn't actually play Paladin, but seen enough from others.

I will say that Oathbreaker should either be chosen at creation for lore purposes. Someone intending to be an Oathbreaker has to pick something else and intentionally mess things up at the beginning of the game, which may also affect party members.

OR

Oathbreaker options should have tags in dialogue leading you GRADUALLY to this transition but letting it be known this is going down an Oathbreaker path.

Larian swung for the fences trying to do too much and missed...as usual...

A lot of their shortcomings really come because they can't just keep it simple and do what is required only.