That 50ms isn't necessarily wasted. When I get the results of that database call I want the results returned to the user ASAP, with async operations the thread may be too busy to do that.
We do this daily in real life. It's more efficient for me to have 10 minutes down time at work while I'm waiting for someone else than it is for me to start something else then either get interrupted or finish another task before I respond to the person I'm waiting on.
It depends on how fast you can switch context. If you can switch context in 1ms, then waiting 50ms is a waste of 48ms. But if context switch takes 100ms then sure, it's better to wait idling.
We do this daily in real life. It's more efficient for me to have 10 minutes down time at work while I'm waiting for someone else than it is for me to start something else then either get interrupted or finish another task before I respond to the person I'm waiting on.