Ok first a disclaimer: Every hero in this game is important, while some may not be as useful (torb,sombra,symmetra) they do have their moments where they shine. Torb sombra and Sym can work well in comps despite being some of the least picked heroes.
Personally I think rein is the most important hero in the game due to the fact that he’s hard to replace. You can argue that you can swap out orisa for rein but there are 2 reasons why I disagree with this
she’s the easiest tank to kill due to her massive hitbox,low health, massive head hitbox, but unlike Zarya with a smaller hitbox and can regain 200 health.
her shield doesn’t last nearly as long as reinhardts because its about the same size (only about 5% smaller) and doesn’t even house half the health.
However despite rein being needed more often than orisa there are moments where she really shines and can be needed more than rein sometimes
Now for the big elephant in the room “mercy is way more important and cant be swapped out.” which I believe is false. however I’d say she’s the second most important in the game.
- mercy can be swapped out for moira: while mercy does get a little more healing dished out moira also can dish out boatloads of healing and she does more damage
- plus moira can deal with a pharah if the soldier/mccree is having trouble taking her out
- finally ana can provide way more healing than mercy if she’s put in the right hands. the game developers have said them selves “ana has the highest healing potential out of all the healers.”
However if you disagree with me or think you can prove me wrong tell me in the comments below and ill respond