Strome has certainly been very impressive, and I think he will be undervalued come draft day since he will likely be on a seperate line from McDavid, and won't have the quality of teammates and PP ice time as his fellow, non McDavid prospects. So far he's just outside of the top ten for me, but he could maybe be top-5 by draft day.
There's no way he doesn't play top pp unit alongside McDavid, he's going to be the second best player on the team and will see plenty of ice time, he may have crappy line mates at even strength, but the otters don't really have any good wingers for next season anyway.