Mbappe, Felix, Sancho, Jovic. Chiesa is 21 but if you want to count him then him too.
I would argue most of this list.
Mbappe I mentioned myself so I agree he is world class, Joao Felix I also agree is world class, watching Atletico's pre season games he looked a class above every single one of our other players in every game he played. Everyone else on that list I would argue against.
I believe you are including Jovic simply because real Madrid signed him, in reality Jovic had one good season last year scored 25 in 40 for Frankfurt but hadn't done anything much before that, he made no impression at all at Benfica, are we really calling players world class after one season??
Again Jadon Sancho is a similar level to Pullisic, he is a fantastic player but again he is not yet world class, he is not near Mbappe or Joao Felix level who even at this age are capable of carrying the entire team, Sancho isn't a regular starter for England. Sancho has to improve consistency and his decision making, many times he still picks the wrong ball.
Again Chiesa is a fantastic player but he's not world class he again isn't on that level yet, again consistency is an issue, he should be contributing more than 6 league goals at a team like Fiorentina where he is a vocal point and plays week in week out if he is to be world class.
Only Mbappe and Joao Felix I can agree are word class players at this age.