It is indeed misleading to say that $80b in value was created, because Uber and Twilio were not Techstars companies.
"The market cap on Techstars website is $7.5B, whereas YC’s portfolio was valued at $30B in 2014" [1]
A more interesting days point (that ignores outliers) is the number of startups that raised a Series A round; and using that metric, you can rightfully claim Techstars to be #1 [2]
[1] https://blog.routific.com/which-startup-accelerator-is-right...
[2] https://mattermark.com/500-startups-accelerator-company/