Snipers, spies. If a pyro manages to get the drop on you and manages to be a "threat", a spy could've killed at least one of you (and probably finished off the medic if he stabbed you first).
No and no to Snoipahs and Spies. I use the Fists of Steel to make the former rage about not being able to kill me with a fully-charged headshot. I am also paranoid and spray everything and everyone with lead just so that there are no Spies. It really works for the most part. Not many here have the Fez, so I can usually hear them decloak before they have a chance to strike.
Plus soldiers, demos, other heavy + medic pairs.
For whatever reason, it virtually never works out for them. I guess we know how to take cover, especially as Medics, check our six, stay clear from the sticky bombs and minigun gunfire when needed, plus I usually destroy any stickies if I see them.
Sounds like a Valve server, or a server with equally terrible players. I don't care how good someone is, against competent players you're not going to get away with only dying three times over the course of a map (at least one that runs long enough for you to get >80 kills), nevermind kritzkriegs and random crits.
Valve servers are probably located somewhere in North America. I live in Poland. Surely I do not play on competitive servers, I guess this game is just not serious enough to ever become competitive. I was probably playing against some youngsters.
And for whatever reason, we rarely play on servers with random crits enabled. They seem to be disabled on most servers, which I don't get. Getting a lucky crit is fun, even if it means that I die more often.
I don't care if I'm the best in the world or not, what matters to me is whether I am able to play well against people currently on the server with me. xD
It just feels good, man. Being able to single-handedly win every single round on a Payload map. But it's so cheap and so easy, we hardly use that combo anymore. My friend practices his Snoiper skills while I prefer to play as classes with a decent freedom of movement, e.g. Scouts, Soldiers.
On communication: meh. I like to have a chat with my friends, couldn't care less about other teammates. We do talk a lot, though. And it seems to me that guys who communicate a lot do pretty well in the game. Though it's not a rule of thumb or anything, there have been many skilled mutes I encountered during my adventure in TF2.