They both grant the Alchemy ability, and Merci even has gear that improves it.

Alan is a special case (Resurrection only happens upon ally death) that works on chance (except for those adjacent to him) and is rate limited (can only work once every 5 minutes, or slightly quicker with gear). It's like... He can occasionally step in to assist when the healers have failed, and that's it.

He's kind of a weird mix of abilities. Resurrection triggers damage and knockback against all enemies on the screen when it works, similar to the damage that Fire Phoenix dishes out when an ally dies (except her Vengeful Fury doesn't mention a rate limit). It's supplementary damage which may occasionally happen in response to something going wrong.

Alan also has that ability that stuns enemies for a couple seconds, which I never really thought much of before but it occurs to me now that this is like a more limited form of Parryfoot that crusaders besides Littlefoot can benefit from. (Parryfoot makes Littlefoot immune to all damage each time an enemy starts to attack, rate limited. Blinding Light stuns each individual enemy for 2 seconds when they start to attack anyone adjacent to Alan, which just prevents damage coming from the stunned enemies.) This is Alan's way of offering a form of backup protection to his allies, like how Fire Phoenix can boost the team's health temporarily after an ally dies.

Honestly, everything that Alan does can fit under the broad umbrella of the "support" tag.

I think with the Alchemy ability the key there is the fact that Alchemy is an ability that the player must choose to activate, then it's only putting out healing for a limited time and it's on cooldown after that. It's an emergency measure to get a bit of extra healing when you're in too deep. It's healing support, for sure. But a proper healer would want a regular ongoing heal instead of relying on an activated ability.

Hmmm... Checking something... It seems as if the healing that Thalia receives from Alchemy does not get doubled by Thalia's "Godly Healing" ability. Interesting.

Checking something else... Alchemy does not have the power to disable Val's "I Work Alone". Which is fine.

Anyway, I've tried to imagine a healer for that seat before and I was thinking that an actual healer in Merci's seat would likely have a standard once per second heal that's a bit on the weak side compared to the other healers (most of them start at 20%, so this would be either 15% or 10%) But they'd have abilities that triple the strength of their heals while Alchemy is active and double the strength of their heals for a certain amount of time after Alchemy stops working, plus maybe some gear for the cooldown on Alchemy so you can get the benefit of their abilities more often. But this would require some active play (or for the people leaving the game idle with an autoclicker running, they'd want to tell it to click Alchemy occasionally) just for your healing output to take a roller coaster ride up and down and up and down. At best, it would be an inconsistent healer compared to any of the others. And at worst you'd leave it to do its own thing without ever triggering Alchemy and it would just be a weak healer.

The point about not disabling Val's healing upgrade makes sense.