This is irrelevant. Speech-to-text costs $0.006 per invocation (for < 15 seconds) [1], or you can solve 166 captchas for $1. There are already services out there which will solve captchas for $0.50/1000 [2], an order of magnitude cheaper. The fact that Google has a service which will do this inefficiently changes nothing about the threat/cost ecosystem. CAPTCHAs aren't about being a perfect defense, they're about increasing cost to operate at scale.
[1] https://cloud.google.com/speech-to-text/pricing
[2] https://2captcha.com/, the first hit I found with the search [captcha solving serving price]
Disclosure: I work for Google on security and cloud, but not on anything related to captchas or speech to text.