Yeah, it was time. Zimmer and Spielman had been given plenty of chances, and it just wasn't going to work. We haven't gotten close to 2017 roster-wise or coaching-wise, and it's time to take a step back and re-assess things. I am impressed the Wilfs were willing to fire Spielman when it sounded like they were going to promote him to a different position.
As for the new coach, I would be looking for a guy who knows how to lead. That may be a cliche, but many NFL teams are having GM-HC-player issues that teams with more competent leadership are avoiding. I'd also like to find an offensive-minded coach who can maintain stability for our QB, rather than have a revolving door of OCs (caused by some being too good at their job, and others being too incompetent).
I hate to be the devil's advocate here... but from what I've read it has come down to ownership in those scenarios. The Giants' owner John Mara values stability over all else, and thinks they have to give a HC at least 3 seasons. Meanwhile, Dolphins' owner Stephen Ross has little patience (3 years without playoffs == unacceptable, apparently) and has usually fired his coaches very quickly. It's been reported that Flores' relationship with Tua is not good and he was pushing hard for DeShaun Watson... it's not the best look when you're trying to ditch your starting QB for one who's in the midst of sexual assault charges.
Still, I like Flores and I don't think he deserved to be fired. Of all the guys fired, he easily deserves a shot the most. Heck, I'd put him in my top tier of HC candidates. Going 5-11 with a practice squad roster in 2019 and then 10-6 with a very young roster was incredibly impressive. 2021 was a disappointment as they started out 1-7, but recovered to finish 9-8. Though if he didn't like Tua, he's probably not going to love Kirk at his price tag...