All they gave up was Moulson. He was a solid finisher for them posting 3 consecutive 30 goal seasons. But played with Tavares, who he was friendly with when he arrived. He just went from the penthouse to NHL purgatory. There's not even a guarantee he'll stay past the deadline. The Sabres are terrible. Both players are in their final year. For the Islanders, it's a no brainer. A full year to pitch Brooklyn to Vanek. I don't know why he wouldn't be motivated. A chance to get back to the playoffs and maybe make a run in a weak division.
The draft picks aren't bad especially if the Isles make the playoffs. All they gave up was a first rounder this year. Second round the next year. It's solid value. But when you have elite prospects like Strome sitting in Brideport, it's worth the risk.