Jets haven't had a 'great roster' for a while. They have completely revamped the roster with talented young players over the past 2-3 seasons.
Scheifele, Trouba, Ehlers, Laine, Morrissey, Hellebuyck, Lowry, Connor, Copp, Armia, Tanev, etc. These are all young players that have either just started or just hit their stride in the past 2 seasons.
Last year the Jets were still bringing along young players and rookies that were still learning the NHL game, and had a horrendous amount of injuries. They also had a sophomore goalie (Hellebuyck) that was struggling with the #1 responsibilities. Knowledgeable fans and the Jets management and coaches knew that this season was the first that they would likely be a legitimate contender, which is why Chevy finally made a splash in UFA went out and picked up Kulikov and Mason, and swapped a #13 pick for a #24 overall to retain core roster players in the expansion draft. Coaches, management and players have all said that after a period of draft and development, this was the year that they were focused on "playoffs or bust". It's not a coincidence that the Jets' big media campaign this season was #RiseTogether.
The notion that the Jets have had a good roster that has just underperformed shows a lack of in-depth knowledge about the development of the roster and the organization over the past several seasons.