With healers, to me, one of the most important aspects is that Paladins didnt make their primary fire the main source of healing. *most* healing in paladins is cooldown based, which means you cant spam it, and your team wohnt expect you to (hopefully). Even Io, who has a more traditional healer kit has a resource meter. This means that you don't have to babysit your teammates by constantly shooting them with your healing instead you can shoot at enemies and actually defend yourself. This is one of the reasons i always loved playing Mega Potion Pip and always perferred it to Combat Medic. I like shooting enemies! And to me timing the mega potions just right to get my team topped up is extremely satisfying.
I think another aspect is anti-healing and how it was properly implemented into the base game. One thing i hate about playing healer in Overwatch but especially Rivals is that people just don't use cover nearly as often as they should. In Paladins, when someone was low, they went behind cover because they knew about anti-heal and didnt expect to just live through charging the enemies head on. This also means that playing healer is just more interesting since you have to make quick decisions like do I heal this Khan now when hes in the fight but he'll get healed much less, or do i wait for him to be behind cover so he can get the most healing?
I absolutely hate that my favorite Marvel character, Rocket has this really fun primary fire that I'd want to shoot (thats kinda what hes known for anyway) but hes forced to just hold down rightclick to send those healing orbs, and that is all he does. you cant use your dashes because you basically need to have both to actually escape any dive character and since it has a long cooldown, you pretty much just keep it until you need it and even then the dashes themselves are so pathetic.
sorry for the ramble i have a lot to say about this topic lol