I will tell you why you are wrong.
Only teams knowing JT would resign with would be keen on giving better pieces than this.
So give me the 2-3 teams JT would be interested in signing with and i'll prove you you are wrong.
For example, As of now, i heard Nashville, TBay, Mtl and NJ as possible destinations for JT
Nashville : Forsberg is better and Arvidsson is debatable. Forsberg is probably untoucheable and wouldn't make sense for Nashville to give for Tavares as they already got a no.1 center in Johansen. So it leaves Arvidsson.
Tbay: Stamkos and Kucherov are better than Galchenyuk and Palat is debatable (while completely different kind of player). Do you think Stamkos would go for Tavares?? I don't think it would make sense. Kucherov?? Kucherov is a top 5 forward in the league right now and his salary is simply stupidly great. It leaves Palat.
Mtl : Galchenyuk
NJ : Hall is better. and that's it. Would he be made disponible?? i don't know but probably yes. But for me, it doesn't make sense that JT leaves NYI for NJ but it is just me.
Other teams in the league have obviously better wingers than Galchenyuk but would they give them knowing JT wouldn't resign with the team?? You can forget about it.
I think the original premise of 'better wingers' is a bit flawed. NYI center depth without Tavares would be abysmal, so the return should include a center (i know the poster you quoted said winger, but the original islanders poster said the return needed a center, it then devolved to how Galchenyuk isnt a center).
I could see Tampa moving Tyler Johnson in a package for Tavares pretty easily. I dont know how the cap works, but i think theyd do it.
NJ is at a weird spot - I dont think theyre too far away, but i dont know that theyre willing to expedite the rebuild (or that NYI want to enter one) and do Tavares for Zacha/Nico +
Montreal doesnt have a center to offer - unles Galchenyuk comes out this season and plays C and kills it. In which case - Montreal has less of an incentive to go after Tavares anyway.
Nashville would probably be a nice destination (Tavares/RyJo would be very nice C depth), but unless its a package built solely on futures, i don't see it working.