You know, I never really thought of it, but this is spot on. Simmons amassed a crazy roster of talent for Grantland, but that's about it.
Simmons success was before Grantland though. His only two talents were identifying opportunities for someone with his gimmick ("every day hardcore sports fan") to be read and heard + identifying young talented prospects he could learn from or befriend (and later in his career, work with to stay relevant).
Dude is a prime example of being at the right place at the right time by being one of the first with a "relatable gimmick" for sports, blending stuff with pop culture, having a podcast and promoting his work on Twitter established him as a relevant figure (plus being a white dude from Boston) that opened a bunch of doors for him. He also took huge advantage of every opportunity he got: a huge podcast, Grantland, 30 for 30 and then The Ringer and Spotify deal.
It didn't matter he wasn't that good of a writer (I do give him points for being creative and trying different shyt, though), never learned how to do a legit great interview and never really having enough knowledge on anything to have takes worth a damn. By the time everyone else caught up to him and there were better at everything he does, Simmons had such a big following that being mediocre couldn't hurt him at all.