But this is where I must strongly disagree with you. For game balance reasons, I think there should be a common cleric spell list and include healing (maybe as abilities, so you don't have to spend spells on it).
This isn't to say that all priests need to heal, but if they're a priest and not a cleric (which I would call a part of the "elite" tier of priests) they're not worthy of being a PC. I don't think it's good for the game for someone to say they want to play a priest, and then when noone else shows up with healing abilities it turns out the necro-priest can't heal either.
I strongly disagree with this, and I can go as far as saying that this way of though is detrimental to the game.
Generally speaking, I can agree if you say that the "iconic Cleric" must heal, just like the "iconic Fighter" must be the a tank, the "iconic Rogue" must be skilled at lockpicking and trapfinding" and the "iconic Wizard" must have blast area spells.
But there must be
absolutely no requirement for a Cleric to be iconic etc.
And there must be
absolutely no requirement for a
Cleric PC (yes PC, not just NPC) to be the healbot, just like there must be
absolutely no requirement for a Fighter PC to be the tank, a Rogue PC to pick locks and find traps, a Wizard PC to fireball foes. Otherwise we'd be playing iconic D&D only, and this is a huge restriction.
If nobody should force another player to play a Cleric or play a tank Fighter etc., then nobody should force another player to play a healbot Cleric.
The only reason to force restrictions on PCs should be because of the
fantasy setting, e.g. if you're playing an Oriental Adventure game, it's plain stupid to pretend to play a robotic vampiric jedi paladin (can still be allowed, but it's group's own responsibility to see if it's still the Oriental game they want).
Otherwise, every other attempt at pretending another player plays only what the group needs while the others presumably are instead free to choose, should die in a fire, because it's not even polite. (OTOH, if the whole group works together to create a balanced group of PCs, that's totally good... but it cannot turn into a "you choose the wrong class, now you do as we say").
D&D has spent now more than 10 years trying to change in order to work without a healbot, and it
does work without a healbot. All you need to do, is dial the appropriate resources to match the frequency of encounter in the adventure.
Then the group must work with or without a Cleric, and if it can work without a Cleric then obviously it can also work with a low-healing Cleric.