You're as bad as Nick. I don't know where this attitude has come from that 3 at the back is not a thing top teams too, plenty do and have done 3 at the back.
Yeah, 5 at the back just generally relies on your wingbacks to offer a lot going forwards as almost a winger replacement. No problem with it but we have a bunch of players and a team in general that wasn't built to play like that. You certainly wouldn't have AWB at rightback for that system and you wouldn't necessarily have Greenwood, Rashford and Sancho getting regular game time.