I dont know where you get your numbers from, but it’s clearly not from a reliable source.
If you go right now on check-pvp website and select all healers spec, dragon, druid, monk, priest, paladin, shaman… the numbers say this for the top players:
25 healing monks
9 resto shamans
8 resto druids
6 disc priests
2 preservation evokers
1 holy pala
0 holy priests
So I really don’t know how u get 90% discs, I also would love to get queues into those discs as the game is more fair instead of losing my brain trying to outheal Mega W monks