I have returned to ESO 4 days ago and yes, i've been spamming only one button in PvP - frag shield. There is no other more efficient damage dealing ability in massive PvP. Single or small group roaming is another thing.
Anyway, this is yet another consequence of ZOS implementing target cap and forcing everyone to stack up together. Spread out a bit, and frag shield will become less useful. But then again, if you spread out you;re just gimping your group with the current state of the game.