I disagree as well but but both of those guys were well ahead of Strome by age 21.
Scheifele was ahead. Ahead of Johansen too. Johansen may have been ahead of Strome in his age 20 season but it wasn't by that much from what I can see. Strome is only 21 days past turning 21 FWIW.
So most of this season was his age 20 season, we haven't really seen his age 21 season.
Johansen's age 20 season was better than Strome's at the NHL level but it was still only 12 points in 40 games. Ahead maybe, but not well. Both split time between the AHL and NHL. Johansen finished the same season Strome is currently in now with 5 points in his last 20 games.
Johansen turned 21 right after that season and that's when he took off. Strome could conceivably do the same. I don't think he will, but I think if he turns himself into an NHLer at least next year he has a reasonable chance of being a late bloomer. But he needs to be on the team at the start of the next season taking a regular shift.
At this stage I'm mostly hoping Strome is a useful top 6 NHL player of some sort. Beyond that would be great but we need something to show for the asset of 3OA even if it's less than originally anticipated.