I find it hard to believe anyone really thinks Gailey was held to or met a higher standard than Johnson. Even setting UGA aside, you have to reach to find stuff like "only record against FBS teams counts" to drop some of Johnson's wins, and then completely ignore things like the complete failure to ever develop a QB or throw away a conference championship to Wake Forest.
Peaking at 11 wins instead of 9 buys a lot. As do some more 8+ win seasons...
Gailey got six years, won 9 once, but still lost that Wake game even that year. Johnson in his first six won 8 once, 9 once, 11 once, and beat Clemson for a conference title. Clearly a more successful start to his tenure, and then he pulled off another 11 win and another 9 year season out of his next 3. When in his tenure would you have said "wow, this is no better than Gailey and pulled the trigger on firing him? There's not a six year period in Johnson's tenure at GT without one of those 11 win seasons, and yes, that buys A LOT of grace for the 3-9/5-6 years (I'm not even too concerned about the difference between 6-7 after losing a bowl vs 7-6 after winning one). Had he had another 4 years of mediocrity instead of retiring? Then we'd have a discussion, if he hadn't been fired at that point.