Three things he needs to improve on.
Stamina, but in part that develops with age, also in how to pace yourself, the lad goes through an immense amount of workload first 60 and he paces himself better with more of a 'team press' etc you'll see him improve in effectiveness over a full 90.
His assists - part of this is for the majority of games he was playing without any genuine cf (Richy isn't one) and on the whole the team is appalling at players hitting sos e in the box with timed runs - throw a world class top level winger into this team and they'd struggle to put up numbers you'd normally expect. But that aside he needs to be more consistent with delivery.
Goals, 4 first season is an ok amount at his age - but you'd hope he steadily improves on this over the next 2-3 seasons, certainly playing from the right badly hurts him in that regard. On the left cutting in onto his right - I expect he'd double his total, and once he starts scoring the confidence will grow.
In short (kinda) I think he's got the potential to be a very top level player, 'average' players don't have a one season jump in performance at his age and in those circumstances and it suggests a very high ceiling on the lad
He does things that exceptional players do. I'm not saying that makes him an exceptional player, but he had that about him. I went very "long" on him when I first saw him play. I remember him being dropped into the derby, what 2 years back by Ancelotti. He kept Arnold quiet that day (no small feat) and had a couple of moments where he waltsed through their midfield, and ultimately didn't get the pass off. But that ability really struck me. Aside from Gomes, on a good day, we don't have another midfielder who would do that (and we know Gomez is up and down).
As for your areas, I agree with you. I'd group 2 + 3 into the same point really. He needs to start adding numbers. Some of it is about decision making, some of it is about learning to be a bit more composed. I think as he gets more confident playing at this level it will start to come, as he got better at it as the season went on. In his 1st season he here passed up shooting chances, he now takes them on more. He strikes a decent ball so should get more shots off, and needs to learn how to position his body properly when he is in on goal to get definite pens/definite shots on goal.
I think his delivery is ok, but needs to be more consistent, just simplify it down, beat the man and hit an area. Honestly though, for him and Mykolenko, and to a degree Gray having Calvert Lewin back will be enormous. It just allows you to beat the man, and whip a ball in, and Calvert Lewin makes things happen.
I agree on stamina, he does need to get fitter still. He puts unbelievable effort in and was flagging towards the end of the season.
I sort of think he has to work out what he wants to be too mate. He can either go a bit deeper, and honestly be a bit of a Gerrard type player from midfield. He likes a tackle too, and the play can go through him. Or he has to play further forward, and focus on goals/assists and learn to get selfish (in a good way). I'd probably prefer the latter.
He definitely has 7 league goals in him as well. See how easily he goes past people. Its funny when he plays for the under 21's, he scores for fun as well, when he's around better players.