...in the same vein that you can buy armor to deal with physical damage - another core and natural mechanic in League.
I'd love to raise a discussion around this parallel, if you have time!
Specifically, the armor vs. physical damage relationship feels less binary than the healing vs. grievous wounds relationship.
Physical damage is, in theory, frequently tuned around the damage you'll deal to the squishy targets, and armor is a way to make yourself more durable against it -- and there are stats such as Lethality or Armor Penetration that you can use to mitigate the defenses in a miniature arms race. This leads to a fairly rich itemization environment in which armor isn't mandatory (since physical damage isn't tuned to be overpowering if you don't have it), but also isn't crippling for those who deal physical damage (as there are almost always targets without armor, and ways to deal with high armor).
Healing seems to lack these levers currently: healing can't be tuned too high because otherwise anti-healing becomes mandatory in a way that armor doesn't (and is harder to access, so it forces more build choices), but also Grievous Wounds can be applied by anyone who opts into it, meaning that you often don't have the ability to play around it. With high GW values this means that healing that is balanced without GW is cut by 40-60%, and there aren't many ways to deal with GW save, perhaps, as a support who can buy heal/shield power.
To me, this suggests that the healing mechanics may benefit from more depth.
Have you considered making more +healing effects, and additionally making GW a more available, possibly stacking mechanic? That way I could see an environment where I could buy more +healing to heal more, but my opponents could counter it with -healing effects, possibly negating my bonuses or penalizing me further without going as far as the large 40-60% hits we have now without specific investment.
It might also allow healing to be better balanced as a baseline, because the difference between "my opponent has bought GW" and "my opponent has NOT bought GW" wouldn't be as severe at lower values. The difference between 0% and 40% reductions is pretty meaningful against healing lane opponents, but adjusting the base healing values and making items like Executioner's Calling more stat-efficient and changing their power to things like -15 Heal Strength on hit might help make healing a more nuanced item space that could be splashed more places -- it penalizes the healing champion less for the portion of their power budget allocated to healing, but also means that opting into anti-healing itemization becomes a more reasonable choice with more options in how you want to do it.
devtrackers.gg