By that logic, Warrior and Dark Knight should be pure DPS and Astro should be a DPS/Support, which they clearly aren't.
XIV doesn't necessarily need to abide by rules set by other games in the franchise and it's not like it's done that in the past, Summoner was never known for debuffing and status ailments but that's their main identity in this game, Red Mage was always identified by its ability to use both healing and offensive magic to great extent yet the healing part of it takes a huge backseat in this game as well, Bard was never really known for being useful and wow would you look at that!
Dancer can absolutely be a healer even if it wasn't one in the previous games.
