GP doesn't necessarily matter, roster focus does. It's possible to beat someone with a higher total GP (which keep in mind is taking into account ships).
One thing I notice is that your roster is starting to go a little top heavy already. Your best team is fairly good at low levels, but not even necessarily the greatest, and they are geared way higher than anything else you have. I don't know that I would've made Old Ben one of my first two g12s. There's no reason Luminara should be at g10 (mine is g8 and level 77, for example). By the time you're able to break into g12, you should in theory have access to much better healers.
Aside from your arena team though, you have a few other g10s and 11s, but not many other geared squads or even characters after that. So your top single squad being so much stronger than anything else you have is going to influence your matchups. Someone might not have their top teams geared as much as yours, but they have more fieldable teams, and maybe with better comps or even mods.