Here's some more of the consequences of having persistent stats based on XP or kills.
After not getting any player kills for a while I checked the scoreboard to see why, and to my (lack of) surprise, the entire other team had switched to my side.
Ok, so I try another server. It's 3v1 so I join greys to make it 3v2. After we start winning "Rulic" joins greys so he can run up his stats.
And again, this time with "Honor us few" and "Sneak" switching to gang up on the losing team.
This happened in basically every game I played today. But this board limits to three screenshots, so I'll leave it that for the screenshots.
In the next game, we capped 3 of the 4 bases almost immediately, causing "Scheiden" to switch to the winning team to rack up more easily kills. In between those games, I tried another active server. When I joined it was 19v19. After I backdoored a base and we started winning and I checked the scoreboard again our team had more people, 23v19. We were greys so the default team for anyone joining when the teams were even was greens, and to my (lack of) surprise again, people switched to greys.
The funny thing about this is that if you're some noob who just joins the game and isn't good enough to single-handedly turn the game around, the team "balancing" mechanism guarantees that you'll join the losing team and get crushed. It's pretty much a guaranteed bad experience for any beginner who doesn't go with the crowd.