Happens to a few nations but England is pretty intense. I'm not saying Greenwood and/or Rashford are bad players. They're good. But I don't get the feeling they'll be elite players. Time will tell.
Agree on Rashford. Any hopes of him progressing and improving start with him being healthy. The EPL schedule and amount of fixtures don't help. The quality vs quantity approach is something I think they need to look into. Also, reduce the amount of EPL clubs by 2 imo to lessen the schedule. It's too much.
The English pundits have parroted into the Premier League's "best league in the world" marketing so much that they've bought into it to the point where they think that succeeding anywhere else doesn't mean anything. I think at least part of that is just laziness at not watching anything else though. In the run up to the Euros I remember seeing German football writers losing their minds at seeing English pundits leaving Sancho out of their prospective England squads. Someone reminded me the other day about when England played Germany in the 2010 World Cup and The Sun ran an article about how no one would swap anyone on the England team for a single player on the German one because they were a team of nobodies. Also that "Phillip Lahm may be a decent right back, but he's no Glen Johnson"
I think another of the benefits of Sancho coming in (and apparently Varane) is that it will allow for more squad rotation. Sancho can play on either wing or as a #10 so there's more versatility there allowing players to switch around for different games so they aren't playing the same lineup every time. And Lindelof will go from starting every game to being a decent enough backup, which is maybe more level he should be at on a squad that's looking to challenge for titles. I do hope Tuanzebe still gets a good amount of minutes though. There's a lot of potential there and he's been really unlucky with injuries over the past few seasons.
Solskjaer clearly doesn't trust basically any of the players beyond his starting XI and so guys like Rashford, Fernandes and Maguire were clocking up a ridiculous number of minutes. I think it was two seasons in a row that Maguire played more minutes of professional football than anyone else on the planet. And Rashford continuing to play so much despite clearly being injured was irresponsible. With how insane the schedule is going to be over the next couple of years I really worry there's going to be a lot of burnouts and needless injuries.
As far as Rashford and Greenwood's potential, I think Greenwood is the more likely of the two to be world class but both could be excellent. But as a United fan I'm obviously pretty biased, especially towards academy players like those two.