I don't think the concept was ever "Marner sucks so the Leafs should trade him" (though I'm sure some posters in the thread have insinuated as much). Young players struggle. The point is that if they choose to, the Leafs could use Marner to acquire a valuable piece that wouldn't be offered for lesser pieces.
I'm not overlooking the premise, it's just the notion that if Marner is ever moved- it would have to be for a clear top pairing defender or at least a young D with clear upside to be one- not one's with huge mental lapses or inconsistencies- i.e Hamilton, Klefbom, Larsson, Brodie types....we'd want a young D with equal pedigree and stability. We already have a guy like that in our top 4D, Gardiner, a guy who looks good, or even a #1 in spurts, but who's inconsistencies are far too troublesome to be relied upon.
It's a very short list of players, guys like Provorov (who I myself wanted over Marner at the time of the draft), Werenski, Jones, Slavin, and a few select others. I'm not implying any of those teams do it, but that's what it'd cost for consideration from the Leafs practically speaking.