Our experience at Google (using first CPython and then Java) was that the single-threaded multi-process approach lead to better developer productivity but worse sysadmin productivity. It made reasoning about the behavior of the code significantly easier and wasted less time searching down race conditions, livelocks, and deadlocks, but it meant that SREs and infrastructure teams had to spend more time managing memory consumption and dealing with deployment and monitoring hassles.
So it's a trade-off where the downsides often get pushed off into another group. As a developer, I really miss the CPython solution, which was a lot simpler and seemed more robust. But then, I wasn't the one responsible for pushing out new code or monitoring. I do think there were various optimizations we could've made to our other tools that might've compensated for the need to run more server processes, and wish we'd tried that before jumping to "Let's use a GIL-free language."