I certainly can't, I don't work for Substack, but I've met a number of people who write using their platform and so far getting an advance seems 100% predicted by how famous you already were for everyone that I've heard about (either personally or secondhand). Which matches the obvious business incentives - if you're a writing platform, the main thing you care about is getting lots of well-known writers. If there's an obvious theory that explains all the data you have right now, we should probably assume it's true until shown otherwise.
OP isn't complaining about the lack of an audience at Substack. OP is complaining about the huge amount of support (aka cash payments) given to already established players to join Substack (via pro) while giving no support of the sort to independent writers. OP also comments that this kind of support ($100kish) is what allows big writers to move to Substack as an independent instead of being tied to a job. While I don't support OP's premise of Substack pushing an agenda through Pro, I'm also not supportive of what essentially are the platform's bribes to famous writers, which the platform uses to market to independent writers as a way to make more money. But I believe that's standard practice anyways everywhere - YouTube Creators get paid to host on YouTube, while smaller creators aren't even paid until they hit thousand subs. But AFAIK, YouTube didn't pay any creators to join the platform outright like Substack does.
