Firstly, Nelson will likely sign for more than 5.5 per year, especially if it's in Buffalo.
Next, I don't think he'd be close to the player here that you describe in your last sentence.
Lastly, this is the kind of contract teams grow to regret.
He may cost more then 5.5 to come to this horrid location but he is not getting 7 mil per. 6 is likely his high end.
And Nelson some how if given decent ice time and line mates wouldn't come close to scoring 20-25 goals and 55 points even though he has scored 19+ goals the last 5 years straight including 2 25+ goal seasons. He finally got more then 15:30 a game in ice time and scored 53 points. Has been damn good this post season and has 2 of the 4 GWG for the Isles.
Moulson
Okposo
Now Nelson... nope.. done with the Islanders player experiment
Because he plays for the Isles that automatically disqualifies him? Nelson didn't get to get carried by Tavares. He is a 20-25 goal scorer on his own getting 16 minutes a game. Nelson is nothing like Moulson or Okposo.
Good luck finding a quality 2C without either trading several assets, several mil per in cap space or both. 7 mil for Hayes is applauded around here but a hypothetical 5.5 for Nelson is somehow Moulson 2.0
Nelson is a very good skater and fast. Moulson and Okposo are very slow and are horrible skaters. Nelson is not a star but please, he is easily the 2C on this roster and would be the 4th best forward. This team had 3 forwards who scored 20g and 50+ points. And that will go down to 2 when Skinner likely walks. Nelson did both. Oh and his zone starts are skewed heavily in the DZ. He only has 1 season in his career where he received more ozs then dzs, so it cannot be said that Nelson is only productive due to linemates, deployment or PP.
100 of the 123 career goals Nelson has are at ES. He has 5 straight 19+ goal seasons. He had never gotten 16 minutes a game prior to this season. A fast good skating 2C who will score you 20 goals and 50 points mainly at ES is clearly not needed
Pickings are slim in free agency, unless you think we somehow can convince Matt Duchene to sign here (while paying him 9+ per). 5.5 per for 20-25 goals at center is fine. Does not even come close to Okposo. 5.5 per in 19-20 is far more affordable then 6.0 per in 16-17.
When you have literally 2 20 goal scorers under contract for next season it is pretty comical to turn your nose up at one who would only cost cap and not assets. Nelsons skating ability means he will continue to score 20-25 goals a season for the next half decade. Okposo and Moulson hit a brick wall in their early 30s because they are awful skaters.
And Kevin Hayes at 7 per is not a better option then Nelson for 1.5 mil per less. They are nearly identical production wise. Both have their first 50+ point seasons this past year. Hayes has 1 20+ goal season and Nelson has 4. They are a year apart. Hayes has size, Nelson has speed. We shall see though if Nelson continues to have a quality post season I doubt the Isles let him walk.