Actual question... how would you compare this guy's success pre-GT to CPJ's pre-GT?
Sub FBC level Johnson has it. What he did at GSU, both as OC and HC, is up there with the best accomplishments at that level compared to just about anybody. 86 win% overall and 90% in conference as a head coach and two championships with 2 more as OC. Chadwell at North Greenville was good, I believe the most accomplished coach in their history, but not to the same level. At Charleston Southern, Chadwell took a team that had 3 consecutive losing seasons and won, 10, 8,10 and 7 games. So that is a better building job, as head coach, but not the same level of success as johnson had.
At Navy, Johnson took a team with 4 consecutive losing seasons and won 10 games once, 9 games once, and 8 games three times in 6 years. Meanwhile, Chadwell at Coastal is a little weird since he was interim for a year before going back to OC for a year before becoming HC permanently. Anyways, he primarily saw them transition from a powerhouse FCS team to FBS and after the first 3 years struggling, with 3 wins (as interim), 5 wins (as OC), 5 wins, he broke out winning 11 games back to back and currently at 7-1 this year. Overall, while what Johnson did was impressive, I think you'd have to say that Chadwell is more accomplished at the FBS level.
Overall both have proven to be able to take a struggling program and build it (Nave and Charleston respectively) and take a pretty well off program and push it to the highest (GSU and Coastal). One thing to keep in mind is that at coastal, Chadwell doesn't really have the opportunity to win national championships. I'm not sure how you'd compare going 11-1 there vs 13-2 at GSU. Obviously the GSU teams won championships, but if the coastal teams in 20 and 21 had similar playoff opportunities against similar level teams, they very well could have too. To me, the comparison is about how good they would be as a hire here, and in that comparison I think it comes down to how relevant you think Johnson's time at Southern was.
To me, the biggest difference is that Chadwell is 45 which is the age Johnson was when he was hired at Navy, and IMO Chadwell is less married to his offensive system than Johnson became while here so I think he'd be more willing to evolve it as need be than Johnson was later in his career. I think if we hired Chadwell it'd be like hiring Johnson when O'Leary left. Hiring Johnson when we did was a good hire. Hiring him 6 years earlier would have been a great hire due to the nature of college football changing in the 2010s.