Watergun Rock Blast Omastar as a Legendary Bird Raid Counter?

I unfortunately don't have a Rock Throw quick move Omastar.

I have a level 30 Omanyte I will evolve to an Omastar tonight and hope to get water gun rock blast. How do you guys think this will do against the birds compared to Golem? I don't want to power up 6 Golems to battle raid bosses if I don't have to.

I heard that the raid bosses do so much damage that you can usually spam 3 bar charge moves, so I was thinking maybe Omastar is viable?

Final question, if I fail getting rock blast on Omastar, is it worth using a tm to try to get it?