Shafted? Lies! Well maybe a little bit...
When it comes to manual PvP I suggest you look at LH of Thebes.
Actually in my head I picture cannon mains doing better in PvP compared to PvE. Due to the fact that they got the 'cannon' role filled in (a generic stunDMF has inventor + cannonneer: you already cannon taken care of, so you're free to put another merc in \o/)
I guess in PvE your strength lies in your mercs :v Since you're the supporting guy that debuffs defence.
I do agree though, that they need at least a strong single target magic (no, not Deadly shot)