I found YC to be extremely valuable for all the reasons I shared.
A side story: After I sold my last company in 2013, I met a guy (who worked at the acquiring company) that had big startup ambitions. We were on a bike ride one day (probably around 2015) and I told him I was going to apply to YC the following year to do a startup. He scoffed, and said the same things as you above — “YC is for young founders w/o experience.” He said he, too, was going to do a startup, but not apply to YC.
Fast forward five years. Armory is growing very fast. My buddy is unemployed after spending $350k of his own money attempting his startup.
Was YC the difference? Impossible to say. But I know my story is true, and I’m thankful for the intense focus YC provided — even for a startup veteran like me, with a successful exit, who didn’t necessarily think he needed it.