No, no it hasn't.
One player can't be everywhere on the entire map at once. Stop exaggerating.
You mean the
Huo-Long Heater? The part where if you rev / fire the gun, flames are deployed, WHILE EATING 6 AMMO PER SECOND? Okay. That's random. Right.
Melee attacks tend to crit a lot. Engineers are no different. My advice? Don't get hit.
I've never complained about DR, but I would assume they're doing so because you can damn near have 90% uptime on the effect, if you use it then cancel and run away. That's annoying. Not overpowered, or anything, and only if they're running Spycicle. And yes, you're right: DR is the only "good" watch. If you're using Cloak and Dagger, you're spending far to much time not contributing.
I assume this is just because a bad couple of games. We all complain at one point or another, but at least make valid points when complaining, such as how much of an anti-class a Pyro is to a Spy...complaining about a mechanic such as the Huo-Long Heater, which is a direct downgrade (in regards to stock Minigun, on a map such as a CtF) is ridiculous.
I can't figure out what this is supposed to mean... I assume you're saying that they've added a lot of guns and it's not balanced. If that's what you're saying, I simply disagree. Some weapons are annoying, but the ONLY weapon I complain about and feel that they're overly overpowered is Stickies. If you use them defensively it is rather impossible to die.
MvM was, and is not, fail. It is a lot of fun, provided you play with friends / competent players. And, even IF -- which I don't -- concede that MvM was "fail", it doesn't detract from the game. If you don't like it, don't play it. Simple.
So...yeah. Stop complaining about a class that one shots.