I agree that Belichick is a genius... who gets the most out of second-tier players.
That said...
Kyle Van Noy was regarded by a ton of draftniks as a star. The Lions did what the Lions do (waste talent) and Belichick smartly picked up Van Noy. It’s very similar to what happened with the Steelers and James Farrior.
Danny Shelton has a similar route: drafted by the Bengals, wasted away, and was signed by Belichick.
The McCourty twins, Patrick Chung, and Jamie Collins were all former Taperiots who left for big money. Once they got paid, they came back to the Taperiots for far less than market-value. Maybe Belichick is a genius in the sense that he is able to get guys to play for less money...
Stephon Gilmore was the best (most consistent) CB in the NFL. Belichick smartly traded for him.
SUMMATION:
Belichick is smart... but, his roster is also quite talented.