Where you get drafted in the baseball (HS players) and hockey drafts is less informative than football because of the ages.
18 year olds will have a range of physical development, and you're drafting off what you saw of them at age 16 and 17. So you'd expect more mistakes due to late growth spurts, etc. In the case of Myers, in all sports relatively taller players often take longer to develop body control, especially right after their major growth spurt.
While 12 games is a small sample, when you almost match the production of the previous 100 games in that sample, statistical theory would suggest there's a low (but not zero) probability that he has the same skill level that he demonstrated the previous two seasons. On the other hand, I wouldn't project that he'll finish the year with 25 goals either.
If he approaches the numbers Sanheim put up last year:
67 15 50 65 +27
you'd have to say Myers is an absolute steal.
If he puts up Morin numbers from his after draft season:
54 7 24 31 +12
(to match Morin, Myers need only go 2-19 21 his next 42 games)
you'd say he was a prospect, but how good of one would depend more on his defensive prowess and how physical he plays.
Point is Myers has done enough already to suggest he should have been drafted in the middle rounds, how good of a prospect he actually is will require a full season to evaluate, but given his size and skating skills, the fact he's shown some legitimate scoring ability makes him worth watching more closely.