I feel you, Zom, because I've been there. The thing about MMO's is that there's so much unfairness and hooligans can get away easily. You just gotta keep on playing until you meet the right people.
For BG's, I notice Alliance frequently win more during peak hours but this does not necessarily mean they have PvP-ers with better gear. It means they are better coordinated so it could be better if you play during that time slot. I can't say much about arenas but just by observing at Deathwing's PvP, the community is toxic as hell and I understand the lack of teamwork and enthusiasm. What I can suggest is to find an arena partner who is actually nice. He/she may be a noob, but at least the fights will keep you happy and motivated to improving.
I haven't been into a guild that utilizes DKP because I just refuse to abide with complicated systems. But believe it or not, I was still able to reach 6kgs back in Lordaeron. Sure, it took me 5 long months to reach that level but hell it was worth it! In spite of my hardwork, I still couldn't join RS and 25hc's because I didn't have the achievements needed :( On the other hand, I notice you're the kind of person who wants fair treatment right away so what I can suggest is to join a more causal guild that doesn't use DKP and at least recommends Raid Call. Progression may be slower but you'll most likely make more friends due to the absence of a reward system (which can corrupt people).
If you'll notice, my advice tends to revolve more on the people you meet than tactics and technicalities. if the games continues to frustrate you, I suggest two things (1) take a break from playing WoW, or (2) find a less demanding alternative such a roleplaying and twinking. Because dude, you gotta realize that this game is supposed to be fun for everyone.