According to Star Trek Online, a single Defiant can take out a Borg tactical cube, whereas a Galaxy cannot even punch through the shields of a low-end BoP without an assist from other vessels.
I don't think you're playing the Galaxy class right in STO.
(Also, why are you quoting yourself?)
I don't play STO at all; I'm not a fan of Asian grindfests. I'm going by STO's own forums, where there exists no small amount of wailing and gnashing of teeth about STO's Galaxy being a toothless tiger.
I quoted myself rather than spam the board with the same exact post.