A context switch in a modern CPU takes only a few microseconds. A GB of RAM costs less than $10. So those concerns, although valid in theory, are usually irrelevant for most web applications.
On the other hand, simplicity in a code base usually matter. Code written with an evented API, littered of callbacks, is usually harder to read and maintain than that written in a sequential way with a blocking I/O API.
You can recreate a sync API on top of an evented architecture using async/await, but then you have the same performance characteristics of a blocking API, but with all the evented complexity lurking underneath and leaking here and there. Seems to me a very convoluted way to arrive to the point from where we started.
On the other hand, simplicity in a code base usually matter. Code written with an evented API, littered of callbacks, is usually harder to read and maintain than that written in a sequential way with a blocking I/O API.
You can recreate a sync API on top of an evented architecture using async/await, but then you have the same performance characteristics of a blocking API, but with all the evented complexity lurking underneath and leaking here and there. Seems to me a very convoluted way to arrive to the point from where we started.