So no one on the other team has anything but full Champ/Battlemaster Gear eh? No one else just got to 50 too and only has the equivalent of 6 champion bags worth of gear huh? Can I assume then you are the last person on your server to hit 50 then? And if that's the case, doesn't that make you kinda slow, perhaps explaining your constant stream of defeats?
When I first turned 50, before I had any PvP gear, I too noticed that my attacks where doing ~10% of their damage to certain individuals. You know what I did then? Stopped attacking those individuals and drawing attention to my newbie self, instead choosing to spend my cooldowns fighting those toons that didn't resist 90% of my damage.
Perhaps you've just been unlucky and keep getting queued against Valor 60 premades, but statistically (insert derpa argument about Imps farming Valor on Ilum, since there are 100x the Imps vs Pubs on every server amirite? O except your an Imp, so your side should have more stuff), both your squad and the enemy squad will have the same ratios of people with Battlemaster/Champ/Centurion/No PvP gear on both sides. Math and population distributions are wonderful things.