I don't see why Robertson couldn't bump Mikheyev off JT's wing. Mikheyev is a good player, but his style is so much better suited for a third line on Kerfoot's wing, giving a high speed forechecker and puck retriever to a line that's going to grind a little more than pass tic-tac-toe for goals. Tavares is already an elite puck retriever, so that line doesn't need a Hyman type nearly as much as they would be served by having another high-quality triggerman to convert the Marner feeds.
Maybe they ultimately decide that Robertson isn't ready or needs to cut his teeth lower in the lineup, but I think that stylistically it makes most sense to put the scoring winger on the line that's going to score more goals, and put the grinder on the 3rd line. I think that Robertson can do it, based purely on the fact that I hope it is so
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If Robertson makes it onto JT's line within the first 10 games and stays there, I think he could crack 30 points in the 56 game season, which would be tremendous for his age. I'll save the grandiose predictions for next year!