I agree with you completely OP, although I also feel it's not just about speed, but lack of communication as well. Such is the case when you have randoms working with each other, and not communicating with each other.
... and then there are the trolls, who's only intent is to throw the mission by killing whoever it is about to deliver the document, or the trailer, or kill the target, etc... I've been a victim of said troll once or twice.
But then, even if you DO get on the mic and communicate with randoms, do you think it's gonna be any better? Everybody wants to be a leader, so the only difference is that you get earf*cked while players still act chaotically... there are exceptions where randoms have come together to pull it of as an organized group, but it's rare...
I'm guilty of the same actions, which is one reason I either roll solo or run a mission with a friend; so we can be organized, and get it done tactfully, not chaotically.