Trading Marner in mid season is going to be very hard considering his cap hit. Additionally, he has an NMC.

Trading Marner for Pesce 1 for 1 (assuming thats what you meant) would ensure Tree never works in the management field ever again

Good points.

I don't know if the cap situation works for any team here. They're all adding 7 mil so they would need to make additional chemistry destroying moves.

Marner is anchored on that deal mid-season unfortunately.

Many commenters on here last year and even through Sportsnet forums suggested such trades last year for either Marner or Nylander.

This is not meant as serious but to show why such trades would not help. Ie read the description. None of the trades listed will help.
The only one where has a decent start point is Dobson if he shows he can keep up his play.

All trades were bad and did not consider cap hits. Last year on this site and on Sportsnet I saw many trades like this suggesting like it was the best fix all and they involved Nylander or Marner.

This is meant as a joke ie the description and to prove that way more is needed to even consider trading marner or Nylander.

In the offseason, reports said Tre listened to offers for Nylander but none involved both a forward and potential high end D to make is worth it to even listed. None even involved a high end D one for one.
Hence why is wait to resign

You're definitely right, that trading Nylander or Marner for a defender was/is not the solution, not that there was a trade to be made.

I don't think Dobson would help too much overall, best case scenario is probably that they end up being in more or less the same position, producing offensively (even if it's more contribution from the backend) but still needing help on defense. Assuming Dobson continues to produce, the Leafs would likely be able to sing a top 6 F who along with Dobsoin would have more points than Marner alone or Marner+ whichever Leafs defender gets let go, but it doesn't necessarily mean that that the Leafs would be scoring more or have a significant increase even if they do. The only thing that would work is if the Leafs could get someone that is a combination of Dobson+Pesce (i.e., a #1D or a #2 that could serve as a #1) but those types of defenders would not be available in a trade to your point.

U do know Marner got a full NMC right?

And why would the Leafs trade him if they had the chance to move Willy whose value was sky high this season

Through everything we have seen we know whats coming

Matthews, Nylander, and Marner get extended and either they sign JT to a cheaper 2-3 year 5.5m deal or move on

Expecting 12-12.5m x 8 years

Firstly the Avs don't need a wing. Secondly they couldn't afford the cap hit. Thirdly they couldn't re-sign Marner so he's a rental. Fourthly they aren't giving up a young cost controlled top 4 D of Byram's calibre to do so.

Also why would the Leafs do it anyway?