Something that has unbalanced the game are excessive cures mainly from cool zero, but we understand that it is extremely fragile and without mobility, that gives it a balance. But the idea is to have a mod for all the characters that cut the cure by 10%, this is already something that gives a sense of balance against the massive healing of the game
I don't think healing needs a nerf. One reason being the game even in the tutorial emphasizes that your team should focus the healer initially to disrupt the enemy team. I think by having good healing, it punishes teammates who try to lone wolf every situation in a team based game.
I do like your suggestion of a mod that cuts healing effects by 10% though and believe that such a mod would assist in the overall balance of the game.
What Kam said. Healing generally feels fine, since it emphasizes the team aspect of the game. What I would like to see are some healing reduction abilities/mods.
One thing I thought of was a "Bleed" status that would cause relatively weak damage over time, but lasts a good while (about 5s) and reduces the effectiveness of healing.
I think the healing debuff system for this game is a bit janky, the buttercup mod which applies a 25% healing reduction while in her oil was disabled for a while because of something wrong with it, which was likely the same thing as the Maeve heal debuff mod, which is that it can persist throughout the match after first application, so they may need to be careful adding this modifier in the future. As for bleed, Daemon's shurikens apply a bleed effect whcih stacks with multiple, with the clinger mod it adds up to a lot of damage.
Realistically though, healing is fine in my opinion, Kulev can't burst to save someone and his shield is a fairly long cooldown, Miko can spam burst with chain heal fairly often but can also be burnt through or negated by good focus, and ZC can heal like a boss, but is a squishy target and should always be the main target whenever people face him, especially Daemon.