Can you expand what ugly stuff they're doing internally? I mean, synchronous code is the most simple way to do anything. POSIX API is synchronous by default. Why would you need ugly stuff? Asynchronous API might force you to do ugly stuff (e.g. for files or DNS).
Let's say you are using a low level networking library that is async to the core, like hyper or quinn.
Then you will have some ugliness at the boundary. You might get by with just spawning a current thread runtime to use your async lib, or do something like blocking channels if your low level library spawns long lived tasks.
If your low level libraries are all sync, then there won't be much ugliness.
