Well, to be fair, it has gotten better recently. Tony Ferguson has some decent skills, and both Diego Brandao and John Dodson seem like they'll be legit. But yeah, for awhile, TUF was just turning out guys who didn't develop AT ALL after the show. Mac Danzig, Amir Sadollah, Efrain Escudero, Ryan Bader, Ross Pearson, James Wilks, Court Mcgee, Jonathan Brookins. That's 6 seasons of winners who have made little impact on their divisions. Even this past season...I like Michael Chiesa...but he seems like another guy who may have a low ceiling. I get that these are prospects, but it feels like these guys are the equivalent to a 5th round draft pick in the NFL. You might get lucky with one here or there. But these definitely aren't guys who are going to be game changers.
I don't follow every movement of TUF very often so I forgot about the Chiesas and such. Brandao is OK...nothing special but Dodson looks like he could be pretty decent as a boring Demetrious Johnson-like fighter, with worse wrestling.
Personally I think guys like Rony Jason on TUF Brazil turned out better than most of the guys on the last couple seasons of US TUF.
Also, I think it is unfair to compare Sadollah, Escudero, McGee, Brookins, etc. to guys like Sam Sicilla. Most of the other names are still in the UFC after years and can be tough runs for plenty of mid-level guys. The Sicillas and such aren't ever going to reach those heights.