I'd expect any python codebase which tries to use async/await based co-operative multi-tasking for concurrency at a larger scale would inevitably run into long-tail latency walls -- not just once but repeatedly as the codebase grows/changes.

The potential for a code change or addition to produce unexpected synchronous blocking (potentially with GIL held) _somewhere_ seems really high and I have to imagine it would be very hard to avoid in the context of a real application codebase ...