I think you're overrating Marner/Nylander.
Actually, I think its moreso that you're underrating the amount of value Dmen have. Especially very good Top 4D. The Hall/Larsson trade was the first indication of the massive difference in value between good Wingers and Good Dmen. But it was further proven when Drouin(And established Top 6 and borderline Top line Winger) was traded for a D prospect that has barely even seen NHL action at this point.
In a vacuum, Nylander/Marner are better players than the likes of Vatanen/Pesce/etc. but in the NHL today the premium on Defense is clear and if you're gonna acquire a teams good Top 4 guy it would take Marner or Nylander right now.
Just like how the Avs are looking at moving Duchene/Landeskog and are probably only going to get a Murray/Carlo/Fabbro/Maatta type of Dman back in return. Dmen that aren't even Top 4 guys at this point in time.
I think it's a big reason why trades are just not materializing at all in the league right now. The teams that have Dmen potentially available for trade are demanding extremely high returns, and the teams looking for those Dmen are reluctant to pay that price. Which is also why I dont think Toronto will trade for a Dman and perhaps they shouldn't do it anyway.
Methot was just traded for a 2nd and C prospect
Theodore was traded to vegas to NOT take manson/vatanen
Drouin (who isnt as good as marner/nylander) returned the 2nd best D prospect in the league AND a 2nd rd pick
I think you are looking to much into the Hall-Larsson swap.
If the leafs moved either it would be more of the Jones-Johansen type meaning they have to get a young guy who will no doubt be at least a #2. guys like Vatanen,Stralman,Montour, Pesce etc don't fit that build.
not to mention hanifin who you apparently think marner/Nylander + doesnt return (check the canes boards to see how wrong you are on that one. they would trade anyone not named slavin for marner).
we keep hearing the same dialogue about marner/nylander but it aint gonna happen. how many top 4 D are there in the league?
How many impact 19-20 year old forwards are there? probably about 10x less