Actually, they’re nerfing healers in 10.2 because they think healing is too easy.
There’s a whole thread of outrage in response, over in the PTR forums:
https://us.forums.blizzard.com/en/wow/t/healing-throughput-and-mana-generation-in-guardians-of-the-dream/1666444
And apparently Blizzard thinks healing is too easy because of guys like this, who’s saying over on wowhead that healing is too easy.