Mack did leave some crushing holes on the depth chart that started manifesting themselves immediately, what with seniors leaving after the 2013 season and Ash going medical at the start of the 2014 season. That excuses a significant number of losses in the rebuild that followed. But Charlie ultimately wasn't able to give the program a clear direction and sense of progress. Part of that was bad coordinator hires and the chaotic shifts that engendered over three years. But I think that's ultimately just a symptom.
As much as I hate to say it, Charlie just doesn't seem to have a stable vision of what he wants to build, an underlying philosophy that informs and integrates schematic choices, recruiting targets, game planning and in-game decision making, etc. At Texas, and now at USF, too many games seem to just sort of happen to him, for better or worse, and he just watches them unfold rather than imposing his own clear choices on them. It's weird. You'd think someone with his overall resume and testimonials from successful coaches wouldn't be like that, yet he is.
So even if Charlie left the program with a little more talent than Mack did, no cake could have ever been baked because there was no recipe. Herman had a tough job in 2017, particularly at OL and QB, but we see progress because he does seem to have a vision. I hope it works out.