"just sit at a set all day and hand out Heal Others"
No no no, you gotta swing your stick like a nunchaku in order to support and gain exp (and heal at the same time). :-D
Early in the game, yes. Hell, I typically sell my charged bolt staff at the start of the game to fund another ID scroll and use the Warriors Club.
After floor 8, when sets become more perilous and the Sorcerers to-hit really starts to wane, it becomes questionable. I then typically switch to tagging enemies with Fire Bolt or Telekinesis from a safe distance (preferably with a staff, I try to conserve mana for my main spells and Mana Shield), unless I have a to-hit booster or a weapon with innate elemental damage such as Immolator.
Even then, if I don't have Mana Shield by then, I'm uncomfortable putting myself in harms way unless I know our set is safe. After 20-21 I typically let the Warrior (2-man Warrior/Mage games are what I've played most) get all EXP and simply support the team with magic as needed.
The seven essential spells in my book are:
Everything else is niche or can be done without, but these seven are non-negotiable, must-have spells at some point.
I should also mention (a bit of high-key bragging, sorry) that I have six Triple Crowns under my belt: Two 2-mans with Warrior/Mage, Three 3-mans with Warr/Mage/Rogue, and one 4-man with Warr/Warr/Rogue/Mage. The second Warrior had Grizzly.
Here's a clip from one of my games with Baba and iMoto, where we had an absolute disaster on Hell 12. https://www.twitch.tv/baba_nim/video/22134094
We had really bad desync that entire game, and both Baba and iMoto accidentally went back up the stairs, which we think is what caused that bosses premature activation. It was just a really bad spot altogether, honestly.
And another with Baba and iMoto from our Warr/Warr/Mage game on Nightmare 13. https://www.twitch.tv/baba_nim/video/37479534
We don't even know what happened there.
And another disaster with Baba and another guy: https://www.twitch.tv/baba_nim/video/262620224
Baba and I had some very...interesting games, to say the least. All three of those games went the distance though, cleared all three difficulties.