Cristobal wasn't interested with Diaz was hired. He was one year in at Oregon and there was no way the Ducks were letting him go after they'd just done one year with Willie Lump Lump before he bailed out for Tallahassee.
Mario would've been an option when Richt got the gig late 2015, when he was at Alabama—but at that time Richt was a better on-paper hire as Mario's only HC experience was FIU.
Fact remains there aren't a slew of guys interested in this job and aren't a lot of big named guys available. Look no further than OU turning the keys over to Lincoln Riley or Ohio State giving to an inexperienced Ryan Day the gig when Urban Meyer stepped down—instead of either program going for a big name guy—speaks volumes based on big names available.
Florida State settled on Willie Taggart when Jimbo Fisher took off—aTm WAY overpaying Fisher as they wanted a "big name" guy, who is underachieving thus far—and Florida settled on Dan Mullen; a decent B-level coach but certainly not a home run hire.
LSU stuck with Ed Orgeron, who isn't anything without his assistants. Tennessee has more athletic department money than God—spending $5M annually on recruiting; third in the nation—but keeps whiffing on their guys; Derek Dooley, Butch Jones and now Jeremy Pruitt.
To the original point; if I had my druthers, I would've liked to have seen Butch Davis rehired in 2015 when Richt got the gig. 63 years old at the time, mended fences with UM and went public with the apologies in "The U Part 2"—which came out around then and had him front and center again for the first time in years.
Once Miami passed on Butch then, I was happy with the Diaz hire in 2018. Manny revamped the defense quickly over three years—rebuilding a hot mess that Golden / D'Onofrio left—and that side of the ball looked like old school Miami for a while now.
Any outside hire beyond Diaz—again, who was available and wanted the gig? Can't think of anyone out there who would've been a good fit or worthwhile hire in 2019 as this job simply isn't as desirable as our fans think it is.