I think Ali Mac hit his straps after a season, (difficult because of COVID) same with Bissouma and Caicedo post loan. Baleba looks the part this year as well.Why is it too long? How many players that have never played in the Premier League before come good in their first season? Some, but not many, even ones that go on to be top players. Even Ronaldo struggled a bit initially! Ali Mac took 3 seasons to really get going. I think Kadioglu would have been a hit this season if he hadn't have got injured. But the vast majority are always going to take a season or two.
It's very rare we sign a young player that is an instant hit at this level. Mitoma was, but has he really pushed on from there? I don't think so, he wouldn't be with us anymore if he had. 1-2 full seasons is a reasonable amount of time to make a judgement on a young signing. And when you have 5 or 6 of them in the same team? Even longer.
Mwepu did well within months. JPvH took a few games to warm-up, but was effectively a year after a loan. Trossard was relatively quickly though slightly older.
Normally, there is more a of a second season dip rather than improvement, particularly with younger players.
A season is about right (as we discuss it) but some of those above were a lot cheaper than this season’s, therefore I would anticipate them being further ahead in their development.