I always find it strange how people complain about features when the real problem is that they simply don't like how people use the feature.

Async in C# is awesome, and there's nothing stopping you from writing sync code where appropriate or using threads if you want proper multi threading. Async is primarily used to avoid blocking for non-cpu-bound work, like waiting for API/db/filesystem etc. If you use it everywhere then it's used everywhere, if you don't then it isn't. For a lot of apps it makes sense to use it a lot, like in web apis that do lots of db calls and such. This incurs some overhead but it has the benefit of avoiding blocked threads so that no threads sit idle waiting for I/O.

You can imagine in a web API receiving a large number of requests per second there's a lot of this waiting going on and if threads were idle waiting for responses you wouldn't be able to handle nearly as much throughout.