I always thought it was telling when you look at our record those years surrounding Gailey.
1997 - 6-10 (Switzer)
1998 - 10-6 (Gailey) / playoffs
1999 - 8-8 (Gailey) / playoffs
2000 - 5-11 (Campo)
2001 - 5-11 (Campo)
2002 - 5-11 (Campo)
Gailey wasn't the best coach ever or anything, but he was clearly coaching up those teams.
It's also a testament to the difference good coaching can make.
I don't know if he was coaching them up that much, but he certainly wasn't the main problem. The 6-10 episode with Switzer was just him being a Wade Phillips-like dumpster fire and not caring anymore. He had his ring, he had his money, he was gonna eat hot dogs on the sideline and not give a shit.
The 1998 and 1999 seasons were kinda "pars" for the course -- you still had Hall of Fame talents in Aikman, Smith, and Irvin, you supplemented on offense with some juice from Rocket Ismail and Chris Warren, but the OL and the defense was springing leaks. In 1998, Gailey was a bit of fresh air over Switzer, but even so, all he could coax out of the Triplets was a 10-6 run and a second round loss to Carolina. When Irvin and Ismail both went out in 1999, you saw the offense sputter and the team was barely hanging on.
I mean, sure, he coached 'em up in comparison to Switzer's final year, but I'm not handing Gailey any accolades. That being said, he was... fine.
Then by 2000, Aikman was done, Irvin was gone, Emmitt had pretty much nothing left, and the team was just finished. Especially with no QB, 5-11 was all they could muster. Campo sucked as a head coach, but not necessarily because he couldn't coach defense. He was just completely outclassed as a head man on a team that desperately needed a rebuild and a new direction. He was a yes man and a direction follower, not the man needed to drag that team out of its funk.
FWIW I actually think Garrett wouldn't be so bad as a rebuild coach. As the JJT article hinted at earlier in this thread, "long term" is his strength. Game management on the fly is not. I think that's fair. Which is why I could see him being desirable and actually having some success if he went to NY and coached the Giants.