That's an exaggeration, he didn't leave the worst roster in school history.
Richt's "goodness" or "badness" at Miami is subjective. But what's objective, is that in comparison to his predecessors his record was better than all of them. Richt had ONE losing season at Miami, not 2, not 3, just one. Al Folden had FOUR losing seasons at Miami, not 1, not 2, not 3, but 4.
Whether or not the condition of the roster was left in a good spot is up to the next Coach to figure out. It's their responsibility to shape & mold the roster the way they see fit & produce a winning product on the field. That's why HS recruiting & transfer portal exists. Placing a high premium on how you leave the roster for the next Coach seems to be of high value from your view, but what's more important, is winning on the field. It doesn't matter if you gather all the infinity stones & have a roster full of NFL caliber players if you can't take them on the field from September to December & win with them.
So if you wanna knock Richt for the state of the roster during his tenure go ahead, just stop trying to juxtapose it next to Folden as if he somehow dropped the ball from Folden. Folden didn't win SH*T at Miami or at any place in his career, so there's no reason to compliment him while critiquing Richt.
Whatever Richt failed at in Miami towers over anything Folden did at Miami. So if Richt is considered a bad hire, then Folden was a significantly worse hire. And the results bear that out.