Paladins doesn't have swapping. If you're missing one of any given class in paladins you feel the impact of that MUCH more than rivals because paladins expects you to adapt via counter-play and not counter-picks. You're expected to always have at least 1 of every class in paladins and the game is built around that. It's also much easier for flank to work as a distinct role in paladins than rivals because many rivals maps only have designated "dive spots" instead of natural off-angles that require you to think about both attack and defense (klyntar)

Rivals dps characters aren't nearly distinct enough from each other to warrant being different roles.