Sancho was brilliant on either wing for Dortmund broke into the team on the right side of the attack and was a very creative winger, when he moved to the left he became more of a goal scorer.
Because he clearly felt Utd needed another wide player, given we have loads of guys who can play on the left adding a lad who's comfortable on the right to replace Greenwood was an obvious signing. He also gives balance of a left footed attacking player.
Levels doesn't necessarily mean divisions but the premier league is the hardest league in the world. I don't think Elanga looks ready to play at that level maybe he could play for a team like Southampton or Brentford who develop lots of young talent but he doesn't look like a top 8 level player.
He may be better suited trying to get into a decent Bundesliga club for example still a good league but the standard of defending isn't as high so it's easier for attacking players to learn.
I'm not suggesting he drops down to league one that would be ridiculous but he looks like he needs to go and develop in an easier league.