I always thought of Paladins as the person who like to one trick to the exclusion of all else and just has to put up with being horribly countered all game possibly compared to having a swap.
Its really frustrating when you go all in on a healing build, and it just gets completely shut down by like 3 people on the enemy team picking cauterize. You might be doing something early game before the tier 3 cauterize kicks in, but when it does your build is pretty much useless. During the fight your stuck with your choice the entire round.
Overwatch is for the person who wants to play a variety of things routinely constantly changing stuff around because they get bored playing one thing.