Omastar attacking moveset
Why WG/HP is rated as B while WG/RB is rated as A?
Answers
The rankings do not take into account other pokemons with the same movesets. It only rates that individual pokemon based on the moves' offensive output. For example, Lapras has watergun/hydropump listed as an A rated moveset. However, no one is going to use that for offense when you have vaporeon, starmie, and a host of other pokemon who do that better.
I agree with the first reply, it seems like an error if anything.
Comparing Omastars with rock moves compared to pure water type moves, rock moves give you more situations where Omastar has a type advantage, hence why they're rated higher.
I'm saying rock moves have some sort of a bonus to their moveset rating, hence why relatively, they're rated higher. The part about water gun + hydro pump on other Pokemon changes nothing about the first statement.