The thing with Caufield, if he scores 40, but gets scored on alot at even strength because of his size and defensive work, then it kind of lower his real impact since the negatives is shadowing the positive, a bit like Gaudreau with Calgary, outstanding PP player, but hasnt close the same impact at even strength...
Now Im not saying Caufield cant improve in those areas, but the lack of top end speed for a such undersized kid + lack of size and reach will be an handicap we will have to live with, so thats why it will be crucial to surround this kid the proper way with big talended linemates that will create room for him, in KK you have 1, drafting Holloway would be the 2nd...
While Caufield has huge upside, he comes with some red flags I mentionned above, so it wouldnt be fair to rank him as our clear cut best prospect at this point, IMO.
About Ylonen, kid is indeed one of the most underrated prospects in the world, not only on HF, but he is not even in most top 50 prospects lists from respectable sources... Kid has elite skating in term of speed and agility, has great hands, sharp passing, very good shot ect, he is in the mold of a Ehlers, Nylander... Will need to improve his work along the board and defensive zone commitment, but those arent big issues, like most kid his age, will tend to be a tad too passive without the puck... Overall, his skills level are pretty high, top 6 for sure... Question isnt to know if he will play in the NHL or not, thats when and how dominant can he become... Personally I wouldnt be surprised if he ends up as a top line 70 pts player...