Lol way too much.

What. You just got better and younger. Thisbwould never happen. This is buf entire core minus dahlin

Outside of Karlsson for Eichel it doesn't really make them that much younger. Eichel is awesome but it isn't worth gutting Vegas' future depth for 1 player. The NHL's proven time and time again 1 superstar can't win a cup, you need a group of really good players.

Vegas is at the cap so either most of the Buffalo players get moved for picks or Vegas completely guts their roster moving players that make them as good as they are.

Vegas has lots of good young players, this would hurt their depth in the short term but I don't think in the long run. Vegas' owner has shown that he wants to win the cup now and wants the best players. Eichel is one of those players and greatly enhances those chances for a cup.
As for the cap yes they are up to it but the players moved for these players are equal in fact a bit of a saving for Vegas this year. Even with rfa next year they will be able to keep all of these buffalo players and won't have to move any of their main pieces.
Is it a lot to give up? maybe at first glance yes but to win the cup, No

Yea this would never happen as it is a lot of moving lieces but the Sabres aren't winning anything with this current core and this return would help them start having a winning season and moving forward