It wouldn't. Databases are fast, python is slow.

Network is slow. So you are waiting on the db for most of a request lifecycle.

That depends on how much work is done in stored procedures instead of wasting network traffic and client CPU cycles to process the results.

Network latency within an AWS AZ is <1ms and throughput is in the GB/s range.

What percentage of python webapps do you think are hitting this as their latency and throughput limit?

(Assuming effective DB use of course, i.e. not doing dozens of DB roundtrips to server a single result or getting megabytes of data and filtering on the client etc.)

True... When I measured something similar in a large python app, the biggest chunk of time went into python object serialization/deserialization.

Not really. Look at Techempower web benchmarks.