its pretty clear in the vid that Dark Urge is not aware of their actions until after, they black out and then Gales hand is just there when they come around... for all we know Shadowheart killed him and pinned it on us?

Oathbreaker has to chose to break their oath like any other Pally has the choice to keep theirs... if a wizard casts a charm on you then you wake up next to your dead sister its very bad but not breaking your oath imo
The problem is that you may have a character background planned out, where he/she has already become a fallen Paladin (Oathbreaker), but to play that fantasy you still have to play as a normal Paladin until you can break the oath "again", so that you finally ACTUALLY becomes an Oathbreaker, you just don't go back to being a normal Paladin just because you forget what happened, in my opinion. Others might have an easy time to just ignore that part, but for me, personally, I really struggle to forget such things happened and would always be on my mind playing that character.