To me it sounds like you lost too many games in a row and can't get your teammates to work together to win. Now, i may not be playing on the same server as you but I do play on Quite a few different C4G servers and i've never seen 20+ people that are actually in a coherent group. Maybe 6-7 at most.
I'm not sure what you mean by "Dirty playing/Tactics" but i'm willing to bet there's probably none of it. Just something you haven't realized how to counter it yet. There's really no tactics that cannot be countered in one way or another.
The balancing in KOTH is actually really good. and all teams provided they have proper teamwork can win. Perhaps it's not balancing of the game but the mindset of the people on each team, and not just the team winning.
From my experience, the team that always wins is usually filled with people that have one thing in common - Comms, teamwork, and willingness to work together. Check the team your on for those 3 things and if they don't have it, you can probably see why you're not winning.
Quick edit: As to the comment about people wanting to join the team that has the "Better people" on it. Generally it's because those people want to play with people that are more serious about teamwork and actually talk tactics and use proper comms. I choose what team I join based on the people on the teams - I join the team with the people I most enjoy playing with, and because of the way I play and the way they do, it does seem that that team generally wins a bit more than the typical "Always winning Team"