I've always had the attitude in these team style games that idiot players end up making things a wash over many games. If an idiot is in a game, you only have a bit less than a 50% chance he'll be on your team (unless you yourself are the idiot, heh).
There's a bit of bias that goes on in categorizing wins and losses. Players win because they are skilled and awesome (not because the other team had a feeder), they lose because of poor luck/bad-teammates (rarely because they were simply outplayed).
Hell, it doesn't even apply just to team games. Card games like Hearthstone. Every win = skill, every loss = opponent got lucky. No one ever wins because *they* got lucky. 
I try not to let such things get to me. I just play the best that I can and shrug off losing.
Ahhh, I can agree with this one, a thousand times over.
I've seen this in the fighting game genre about 20 billionty times. When I completely stomp someone, it's always "well if such and such thing had worked CORRECTLY in that match, you definitely woulda lost". Even if it's the 15th time in a row that the stomping has occurred. And of course nobody in that genre can just have matches for fun, it's always super-serious and ya gotta follow the metagame and the tiers and you're a scrub if you dont use the RIGHT combos (even if you're winning like crazy with the "wrong" ones). Ugh. These trends in competetive games are very.... irritating.
Though it's at it's worst when watching videos with commentary in games like Dota or LoL or whatever. I watch a lot of videos of Dota done by Purge, which involves him commenting during matches he had, and even with someone like him who often acts very professional and never goes into rage mode, it's always always always things like: "Well, see, if such and such teammate had done THIS instead of THAT, and if this other thing had been like this, the enemy would never have won that teamfight. We woulda taken them out with ease" and such as that. The enemy is NEVER skilled... it's just allies that make mistakes that cause losses!
I typically do as you do and try to simply do the best I can in any match regardless of what's going on. Regardless of wether we win or lose, my own performance can be good or bad, seperate of that, and that's what I focus on.
And it's rare that I get into what I personally classify as a "good" team. I dont mean "skilled" here, I'm talking more about attitude and such. I had a match in Dawngate recently where we had this one guy who was REALLY new, and hadnt the foggiest idea as to what he should be doing at any given time. But since it was a good team, we all just encouraged the guy to experiment and to feel free to try things out or ask questions or whatever, and learn as he goes. Nobody yelled, nobody insulted anyone..... it was good overall. They're much more fun that way. Too many players forget what "fun" is, and they forget that it's supposed to be one of the points of gaming in the first place.
