I'm a big powercreep worrier, so dropping healing power seems like a solid step to reduce how much stronger players are than monsters (and mages specifically). I am curious about a few things though.
Sapphire identifies spellcaster lean as a main problem in making healing unequal between builds. I think he's right, but also we've got a few spellcaster lean options that are build universal (Wishweaver and Infernal Angel semi rares, and Eternal Champ, and debatably commander Necro (post stat scaling bug fixes at least)). Could introducing more build universal spellcaster leans that appeal to warriors and rangers also solve this problem Sapphire identifies? I'd probably be against this, since like I mentioned at the top, I'm hopeful player power can be cut down to better match how strong (or relatively weak rn) monsters are, but it was a thought I had. I'd also love to see off meta support, like the current FD warrior options pre stat revamp and the 0 Proc weapons that work great for FD builds, and in my mind, warrior / ranger spellcaster would be the same thing. I don't really support this idea, but I thought it was mildly interesting and related.
Big agree that damage shields (barriers mana + chi shields) trivialize a lot, and aren't countered by freedom, boss boost, or damage caps like some other cheesy items we have. Indirectly weakening those options should make boss fights more competitive.
Sapphire also mentions not boosting healing with booster pets and guests, or Sila's Staff or similar effects. This I'm less sold on personally, as all builds have near equal booster access for heal element (you could argue warriors have it best with Oath of Desire, but it's a weak argument IMO mages can and should run it too) (until we get a healing cutlass at least lol). In theory, a warrior casting a healing spell with dual dunamis should heal the same as a mage casting a healing spell with dual poelala. That being said, the reality is most END based healing effects are magic by default, so warriors and rangers, unless they use one of their like 3 special healing spells / skills, can't use boosters as easily. I think this could be "fixed" by spending dev time updating the 5-10 healing spells that scale off END or CHA to follow weapon type for damage type, but that would take dev time. If that does seem like a good course of action, I'd be happy to compile a list of healing effects that scale off secondary stats (so theoretically build universal) or follow mainstat that deal magic damage always, to make the job a little easier.
About the above paragraph, I just thought it was something to remark on, because theoretically, all builds additive boosters should be equal when boosting healing effects, so I'd kinda be against making additive boosters not work on healing spells, but I'm not really that bothered, I just wanted to point it out as a potential counterargument.
My last concern would be about potions. Potions are to my understanding mostly outside balance, and at 250 END, they heal 925 (1042 from END bonus) (621 at 0 END) HP for 100% melee (1 turn investment). Pure healing spells with standard penalties and spellcaster lean (no other boosting effects, without the 1.125 from END) heal on average ~735 HP (source, I was messing around a few days ago and by chance collected a bunch of data on this to theorycraft for Wishweaver shield's use cases). So, if you removed spellcaster lean, they'd heal on average ~535 HP per cast, investing 200% melee. So, no matter your stats, potions would outperform normal healing spells, and cost 0 resources. I'd personally hate to see potions become the meta healing option, because it's just so boring. I don't have a real suggestion on how to fix this though (nerf potions? Buff healing spells while nerfing them? Both seem extremely suboptimal), but I wanted to bring it up. ---crazy solution, buff regen's turn delay bonus (and all turn delay bonuses) so it's a viable alternative to potions?
All in all, very supportive or weakening player healing, and making it more equal for different build archetypes. I'd support keeping additive boosts affecting heals, regardless of their source. I'd be bummed if potions jump back up to optimal healing options