A well-tuned web application layer is CPU bound at scale - your database is well designed and not a source of latency, and the lack of concurrency support in a language doesn’t matter if the interpreter is so much slower than context switches, which is absolutely true for CPython.
There are many sites and services where a rewrite in a new language is just not viable, and I still would recommend Python-everywhere to startups doing things remotely associated with data. So PyPy would be a tide that would lift many boats.
I switched a high traffic Flask web app to PyPy a couple of years ago and we saw substantially faster response times across the board, and much higher task throughput from our background worker machines, many of which were pegged 24/7.
We had so much less baseline load afterwards that we were able to scale down a bunch of instances. The transition only took a few hours of effort fixing one or two incompatible dependencies, so it paid for itself in savings quickly, especially vs an approach of trying to rewrite the slowest bits in a faster language.
There are many sites and services where a rewrite in a new language is just not viable, and I still would recommend Python-everywhere to startups doing things remotely associated with data. So PyPy would be a tide that would lift many boats.