For certain web servers that utilize an event loop instead of threading, it becomes very easy to accidentally block the event loop with synchronous work, so the choice of server does matter.
In other words, having 32/64 concurrent threads you won't get the throughput you want so agree there.
However, I'll elaborate on my point and why it's not just "use event loop".
If you block the event loop you can get catastrophic behavior, like your entire server acts as if it's a single threaded synchronous runtime.
However, even with not blocking the event loop, you need to have optimal IO __given a coroutine__. If you are waiting a bunch of ms for multiple network calls and also a db write within a coroutine, your latency is going to go up and you might not hit your latency requirements.
I was specifying that the architecture was taking these concepts into account and getting low latency on each request in a high throughput way by not blocking on writes, precaching info in server memory, etc.
If they had to go to a db and/or do other calculations per query instead of pre-caching regardless of 32/64 or using an event loop, it likely would have either created another bottleneck or the web server would bottleneck and they would not hit their RPS