There were nerfs to their healing amount? I watched the stream and sure the wound CC on more characters is an indirect nerf to ALL healing supports but per shot Miko is the strongest not even including the poison effect. Only nerf I heard was the 1.5 second light cool down on the fight or flight helix for 15% extra movement whilst taking damage.
Miko has a lot of offensive options - spore shock, pervasive poison and the damage mushroom So in a 1v1 Miko will normally out damage other supports. Mid to late game Miko can 1v1 almost anyone maybe excluding Montana and Attikus if you have access to all mutations (but it’s not necessary).
In short, Miko got off easy this time balance wise so no buff is needed since the impact they have on a match is already immense and needs to be reduced. I mean he already keeps the team alive they don’t need to deal out more damage than they already do plus their survivability is already top tier.