For example, CoinHive shut down.
Just to calibrate a little, I did it on my (midtier, six month old) phone just now and it took three to four seconds.
Granted, Google Apps are disabled, so it may have been one less thing eating up CPU cycles in the background that made others so slow?
Also, automating something in a browser extension is basically the easiest place to automate something because it's just done once per user, with their cookies/sessions/ipaddr, very infrequently.
So that a browser extension exists for something doesn't mean it's trivial at larger scale. I doubt Google cares about the usage pattern that Buster gives people since it alone is not abuse, just normal people filling out the someodd <form>.
With this captcha I feel like I'm just wasting world's energy on useless computations.
Google doesn't care about fighting spam they just want to exploit people for free labor in the name of 'security' just like they are going to kill ad-blocking and fingerprint protection in the name of 'privacy'.
The only way to have it do both is to make you put twice the effort into it. If you are thinking one comes as a byproduct of the other, though, you haven't really thought it through.
Proof of work is trivially parallelizable, and 2^(5*4)=1048576 options are super easy to go through for spammers.
Although I'd certainly prefer something like this being the default approach over hostile measures like Recaptcha v3, which just outright deny a subset of your users access.