That's different, Iruka is the only one who stated that Hiruzen was the "God of Shinobi", and that is his opinion. And In my opinion I don't think Iruka know shit. lol. But unlike Irukas statement, numerous characters have stated that Kakashi has copied over 1000 techs. Including Zabuza, Jiraiya, Yamato, and Itachi. I'm pretty sure there's more but I'm way too lazy to look around to prove a point that is so blatantly obvious.
Again, just because something is used for defensive purposes doesn't mean it can't be used offensively. Look at things like Gaaras sand, and Susanoo. If you remember Kakashi wasn't on the defensive when he tried to Kamui Deidara, so who's to say he hasn't gotten better? And who's to say he won't do it again? Honestly, I think Kamui was meant to be more offensive then anything else anyway, Kakashi just doesn't have the stamina to use it as frequently compared to if Sasuke had it.