The one thing they all need to be consistent with is effort, that's the bare minimum and it seems like this team as a whole is seriously mismanaged when it comes to fitness. I don't know who is in charge of fitness at the club, but they should be the first one to go before any players. As far as Pogba being able to make an impact with a goal or an assist every game or two, that largely depends on who is around him; but there is no excuse when he has a lack of effort. And, I don't think any world-class player would want to be in this current United team. I mean think about it, if you're a great player you want to be in the CL, you want to be competing for the league title every season, so again how are you going to find those players that can challenge for those titles and make them want to stay without at least being able to keep a player like Pogba?
I get what you're saying, how if a player wants to go then we should let him, but Pogba wouldn't want to go if there was a bright light at the end of the tunnel....there's just none of that right now, and how is a new player going to see it any different once they get past the honeymoon phase?
The only players you're going to get that are committed to the cause through thick and thin, at this point, are going to be average players who are just happy to play at United because they wouldn't have that starting spot or even bench spot at other clubs. Every once in a while, you might get lucky with an academy product, maybe McTominay shows some more ability, maybe Greenwood makes the jump successfully from youth to the pros, but that's not a successful strategy long-term if you want to compete against the top teams in the premier league.