A VC once told me that as a rule, Go startups were more likely to succeed than Python startups. Maybe because successful startups are working on simple problems, not easy problems.
There are tons of startups that were built on Python that became enormously valuable companies: Instagram, Dropbox, Reddit, Spotify, YouTube, Pinterest, Quora, SurveyMonkey, Twitch, Zenefits.
I don’t think the data supports your VC’s thesis.
I feel like it has more to do with those VC's having simultaneous investments in Google. Also, the "google pitch" for Go was generally that it was easier for junior devs to get started with, meaning your start up won't have to pay employees as much. Not at all true, of course but investors rely heavily on signaling.
The interesting experiment would be to make Go startups work in Python and Python startups work in Go :)