I've had Ana as either a main or second favorite since she came out and the whole time I've been saying she was broken
That being said, healer choice is fundamentally broken in OW and has been since release. You have these 4 characters who all do the same thing but via a different mechanism. Its clever, and it could have worked, except that OW has other fairly deep balance problems that prevent it from having varied hero choice.
There are 4 groups, from a tryhard perspective, that OW heroes fit into. Attack/defense/symmetra (14 heroes), barrier tank (3 heroes), non-barrier tank (2 heroes), healer (4 heroes). You could get even more granular than this and put Rein in his own category (since he fills a niche no one else does) and Ana (since she take the slot of a healer OR a DPS).
So you have this situation where most of the slots in a tryhard OW team are going to be filled from an extremely tiny pool of characters that have almost no overlap. The misc heroes fit into nice categories, for example Widow and Hanzo. They both provide their team with extra vision, do burst damage to one-shot squish, and use mobility to move vertically but struggle moving horizontally. You've also got Pharah/Junkrat, Torb/Bastion/Symmetra, Genji/Tracer/Sombra, as well Soldier 76/Mcree/Ana. Within each of those categories there's usually a top pick (unless the meta calls for 2 or 3 characters from that category) but there's still some wiggle room for picking between categories. You'll never pick Junkrat over Pharah or defense Bastion over defense Torb, but you might have a legit choice between Genji or McCree if you've only got one slot left.
But healers don't have that dynamic. All of them fill totally different niches, but you have to pick 2-3 out of 4. So of course at any given time at least one is going to be trash tier and one is going to be ubiquitous.
Add all this to the inherent balance problem having utterly dissimilar maps. You can't have a Tracer that's balanced on Lijiang tower and on Eichenwald, its just not in the cards. So like yeah you might swap out that Zen for a Lucio on Nepal, but at the end of the day there's still going to be a meta comp for each map and not much encouragement for deviating from it.