I think the gap is gonna close significantly in the coming seasons. David Gill neglected the academy for too long and it wasn't until Ed Woodward replaced him that we got the ball rolling and revamped the structure and made the correct appointments in key roles. But I fully believe under our current recruitment drive at youth level we will match the likes of City and Chelsea in the very near future.
The coaching at United under Neil Ryan is too basic IMO and from my observation of watching the lads play whether that be on TV or attending the game (I live 15 mins away) he doesn't seem to have a good enough understanding of transitioning play against a organised press or closing the space via enforcing pressure. And I believe when it comes to Semi-finals etc we will be found wanting like we saw against Chelsea who pressed high and Ryan predictably had no clue on how to get the team to transition out of the press which isolated our forwards. The difference between Ryan and Mckenna is day and night from a technical/tactical pov.