I'd agree if AD&D had any other way of healing in a reasonable amount of time, but it doesn't (OK, if you're using 2e psionics there's also the Cell Adjustment power, but that's hella expensive in terms of PSPs per hp). So you need a healer in the group. And clerics are it. And you can't rely on potions because magic items are completely under the control of the DM.See, I've never agreed with that part. Use potions. Hire an NPC healer to adventure with you. Something else. A cleric's role isn't to just healbot.
4e was better in that the role of healer could be filled by any number of other classes, and out-of-combat healing was a personal responsibility. But in AD&D, clerics (and to some degree druids) were it. A cleric who can't heal is like a fighter who's a pacifist – interesting as a concept, but kinda useless.
Of course, that doesn't mean the cleric only heals. They can and should feel free to use the rest of the spell list as well. But it needs to be part of their toolkit.
Depends on what source you're using for your specialty priests. If you're using Faiths & Avatars, where the specialty priests are basically Clerics Plus, sure. Legends & Lore also gives Healing spells to most priesthoods. But if you're using the Complete Priest's Handbook, there are many priesthoods that either don't get Healing at all, or only Minor access which only gets you cure light wounds and slow poison. And there are many priesthoods that don't get Necromantic, which is where things like cure disease and restoration can be found – also vital reasons to have a cleric.I view all of that as completely unnecessary. The huge number of gods, probably a majority, had the healing sphere. If you want to be the group healer, it's simple to pick one. If you don't, then you have all the gods to pick from.
Again, I'd agree if clerics didn't have a virtual monopoly on healing.Just like settings shouldn't all be kitchen sink, generic ho hums, not all gods need to be kitchen sink, generic healer options.