It seems that startup incubators are doomed to follow the same distribution as business and law schools or non-STEM PhD programs: unless you get into a top one (and by "top", I mean top 3 or 4) you should just go home. The connections that will turn your time and effort into something are not uniformly distributed, but clustered around a small (single-digit) number of hubs. The non-hub alternatives exist to take your money (or, for incubators, equity) and are unlikely to return on the investment.
This distribution isn't inevitable, but it's common. For counterexamples: from an economic perspective, there are two classes of post-graduate educational programs where it actually makes sense to go to a middling (i.e. respectable but not top-5) program. 1. Medical school, because the AMA puts a cap on the number of students the schools can take, limiting the number of doctors and keeping the pay high, so that those skills are in demand regardless of geography and connections. 2. PhD programs in STEM disciplines, where students gain marketable skills and therefore, even though the academic job market has been a cesspool for over 30 years, their graduates can get decent private-sector jobs.
Option 1 is not a credible model for incubators, so that leaves the second: some sort of objective and salable value-add. Unfortunately, this is hard to achieve in 3 months in the context of a no-name incubator. The only way to learn business is to do it (opportunity) and that requires serious capital and powerful connections, not a short runway and "mentoring" from someone of dubious credentials.
People learn best when they are in moderate power. Actually, that's the only time when most people learn. Being at the pinnacle or having infinite resources just spoils them, and no one tells the truth to monarchs or billionaires; but being at the base of the pyramid discourages and enervates them. What the connections and cachet conferred by YC acceptance perform is an elevation into this region of moderate power and high opportunity.
I don't think there's room for more than 5 general-focus Y combinators in the US. It would be nice if there were, but the truth is that opportunity and connections are not that abundant... or at least not in that way.