Herbert is considered an outlier in part because he was not only someone Mario inherited but he was already a full-blown starter for the last 8 games of his freshman year under Taggart, completing 63.5% of his passes with 19 TD's and only 4 INT's. Herbert was already an established commodity, not an unknown gem unearthed by Mario.
The problem is the blue-chip QB's Mario evaluated, recruited, and signed at Oregon all turned out to be colossal busts: Tyler Shough, Jay Butterfield, and Ty Thompson. Then he comes to Miami and after saying he didn't think there was a better QB in the country than the one he was inheriting in TVD, he proceeds to hire Josh Gattis and cripple our offense with the atrocity we all witnessed last season.
It's less that Herbert's being used against him and more that everything that's happened after Mario no longer had Herbert has exacerbated his perception as a QB killer. Some fans may not like it and they may disagree with it, but that negative recruiting pitch is clearly resonating with premier QB recruits who won't give us the time of day. If we end up with an Anthony Brown-esque portal QB next season, it'll be pretty clear why it's come to that.