A need is a need. I'm not really sure why you're having such a hard time grasping that. They wanted an elite talent for JT and they got one. The fact that you think it's a foregone conclusion that he walks at the end of the year, or that it wasn't their "most pressing" need, is irrelevant. They're in a position where they can, and should, make that move because it won't have a negative impact on the team.
Again, granted I'm obviously the one having trouble reading, you're completely missing the point here. It's not about me talking about a future player taken with that draft pick. It's about the fact that a draft pick can have nowhere near the impact Vanek has on the ice right now, but more importantly, the impact on the fans who have been patiently waiting through a lengthy rebuild. This shows the fans, and the players, that they're done hoarding "assets" as you like to call them, and are trying to turn this into a winning franchise again.
You're having fun in hypotheticals, but I don't care about that. This helps the Islanders right now, and that's what's important. Not to mention this doesn't somehow preclude them from making anymore deals to solidify other areas of need.