The candidate pool is always retreads and if you look at the current consensus "best" coaches in the league - meaning based on management style and their systems - none of them came off the scrap heap. The orgs that have the Coopers and Brind'Amours went off the beaten path or took a chance on them earlier in their career and cultivated them into a head coach.
GG absolutely deserved to be fired for all the countless reasons I've detailed in previous posts. If you watch other teams in the playoffs move the puck, it is ridiculous how much better at it they are than the Rangers. That's something that's practiced (or not), and that comes from a structure provided by the coach. If the players deviate from the system, you bench them. If Panarin was such a coach killer, you bench him. Panarin was benched exactly once this whole season - for one powerplay - after a giveaway that led to a SHG against.
As for the vibes from Panarin, I get the sense he's someone who's frustrated with his inability to perform in the playoffs but doesn't fully understand why. A coach that had a clue would have looked at how bad him and Vincent Trocheck were together in October, November, December, AND January...and maybe not put them together in the playoffs. I still think that's a huge reason for his lack of playoff production. For all the time they spent together this season, Trocheck scored exactly TWO even strength goals the entire season where Panarin had an assist. That duo spent over 650 minutes on the ice together at even strength this year. You know who else scored two even strength goals the entire season where Panarin had an assist? The illustrious Vitali Kravtsov. In fact, Panarin probably breaks 100 points this season if GG just had the good sense to keep those two apart.
No one has "blossomed" under Gallant at all except Kreider - the players who've taken major strides in their game (Zibanejad, Fox) all did so under David Quinn and have largely stagnated since. Fox's puck movement has never been slower than it was this year. Zibanejad was scoring goals at nearly double the even strength rate in 2019-20 as he is now. The kids all posted career years this season, but I'd hardly consider any of them a smashing success given the expectations of fans and the org. for where they'd be at this point. Goodrow's "career year" under Gallant last year was largely a function of getting more ice time than he ever has before. Then, this year, GG badly overused the 35-year old Kane, badly underutilized Tarasenko who clearly had much more to give than playing 12 minutes a night. He eschewed X's and O's all season, then threw the team under the bus after Game 4 despite the fact that his personnel decisions were a huge part of the problem as evidenced by Game 5's result which featured no adjustments. Then, in Game 6, back against the wall, he changed things and it worked - the team won and got a Game 7. The Devils adjusted in Game 7, and he didn't. When the Devils got the lead, he went RIGHT BACK to what hadn't worked in Games 3-5 and the team got blown out the rest of the way as a result.
Right now, the best thing this org can do is scout other organizations, juniors, the AHL, and even Europe for a coach who has a habit of getting the most out of players - especially skilled forwards. Avoid the retreads, but getting rid of Gallant was ABSOLUTELY the right move.