I'm going to say this.... I think at one point, I'm pretty sure Saban said it is hard to make adjustments during the season. Where do they find the time to fix the issues on defense? They can put short term solution out there, but to truly fix it, you would have to do it in off season.
Check out the old article on how they manage the Game week:
https://www.sbnation.com/a/college-football-preview-2015/coaches-work-week
I'm not trying to say Golding is not capable or that sort of thing, but... I'm just not sure how we got to the point that a lot of people are like yeah, just completely hand the defense over to Golding, but please keep Kelly away from the DC job. If Saban wanted to do that the entire time, he never had to promote Tosh. Golding went from facing C-USA teams, to facing championship caliber teams, that's a big step up.
I also think that's where people, for what ever reason, are selling Kelly short.
FSU faced Clemson and Watson in 2015. They held Clemson to 23 points, their second lowest total of the season. Clemson scored 40 on Alabama that year.
In 2016, FSU gave up 37 to Clemson. Clemson scored 35 against Alabama.
In 2017, FSU gave up 31 to Clemson, while in the process of having a really bad season. Alabama held them to 6 (clearly he's not Pruitt).
Thing is, once you total that up, and he gave up 91 to Clemson those 3 years, and then Alabama gave up 81. Now that's not great, that's not ok let's do what ever the genius says. But it does show that he's capable of going toe to toe with the big boys on defense. So, he brings an element of been there done that, that Golding doesn't really have.
In four meetings with Clemson, the most Kelly gave up was 37 (they gave up 17 in 2014). Alabama gave up more than that to Clemson twice in the past four meetings.