The reason Mitch brother Chris remains in my conscience when discussing Marner, is because of how Mark Hunter at the time of draft used him to sell Leafs Nation on trying to support the selection #4 overall.
Chris Marner had a late growth spurt shooting up to 6-2, so Mark Hunter was hoping that would also happen for Mitch the small undersized winger coming in at 5-11 165 lbs.
Hunter also told us Marner would eventually be moved to centre, in an attempt to avoid the obvious that Centres and Dmen have higher priority building block positions than Wingers do.
Mark Hunter wasted a lot of Leafs draft capital drafting small soft players (which many thought were waisted picks) ie Bracco, Brooks, Dzerkial, Timosov, etc etc.
The issue with the Marner selection wasn't much different, in that the core of the reason to trade him NOW, that he plays too small and too soft and avoids contract, preferring a perimeter game which doesn't translate well to playoff style hockey of hard hitting and tight checking, and physically punishing and if you're afriad to play in traffic as self preservaton from getting hit or hurt, you will not be successful under those conditions.
Now toss in cost.. A winger is the least important building block position (each team 2 X G, and 4 X C and 6 X D and 8 X Wingers) , so now paying Marner more/equal to an elite #1C like Nathan MacKinnon coming off a 140 point season Hart and Lindsey and recent. You simply can't pay a secondary support position ** winger ** then you can an elite #1C that you build strength down the middle. You should be investing your highest Cap into #1C, #1G and Top Pairing Dmen.
Now that Leafs have overpayed Nylander a winger among the best, there simply is no available Cap Space room to build a Cup winning team with a 2nd winger making top 5 AAV. If Marner had been moved to centre in the NHL while playing winger in Junior than investing $12 mil in a elite C, and there would have been no need to every bring in Tavares either.