United's adherence to playing out from the back differs little from the other top teams in the league. City are masters of playing out from the back. Ederson is arguably the best goalie in the world with his feet; their centre backs are technically very sound, and they have adopted and perfected a midfield that mixes it up and drops deep. They are so good at it that most teams have given up on pressing them. The other teams struggle more. Chelsea are just as resolute, if not more so, than United at playing out from the back, and they struggle as much, if not more so than United do. However, as the OP states, our defenders in particular look like they play with rubber boots the way the ball bounces across the pitch slower than a drunk tortoise.
Personally, as if anyone gives a feck, I don't much care for playing out from the back. If there is little press, then it makes sense, but it also stretches the team and puts the team in a more defensive position. If you can lure the opposition up, then hit it long and make sure you win the second ball, you have put the opposition in a difficult position. Playing it slow from behind has little in tactical advantage.