Are Holy Priests bad in PVP or are Disc just too good?

Holy for pvp and raid, disc for m+.

What stats are people finding work best for holy in PvP?

I see some top rated holy priests go all mastery, while others choose to split between haste and mastery.

I guess haste helps with getting casts off and mastery is just more mana efficient healing. But interested to hear others take on it.