Ask HN: Startup Accelerators and Solo Founder self-selection bias

I'm a solo founder and many, if not most, startup accelerator's literature mentions that while they do accept solo founders, they are heavily biased against them due to teams being stronger.

They use the fact that since many teams have graduated from accelerators and become successful, teams themselves must be the driving factor. Or they use some hand-wavy notion (without any facts) that teams *must* be better. However isn't this a prime example of self-selection bias? If startup accelerators let more solo founders in, would we see similar rates of success for startups founded by teams and by solo founders?

I'd like to know on what basis this assumption was formed, if there's any empirical evidence to back it up and if the startup ecosystem gatekeeps solo founders as a result of self-selection bias.