Comment by cherryteastain

I meant the interfaces are horrible. As you said, as long as it has a good interface and good performance, I wouldn't mind.

For example, here's the official tutorial for using the async callback interfaces in gRPC: https://grpc.io/docs/languages/cpp/callback/

It encourages you to write code with practices that are quite universally considered bad in modern C++ due to a very high chance of introducing memory bugs, such as allocating objects with new and expecting them to clean themselves up via delete this;. Idiomatic modern C++ would be using smart pointers, or go a completely different route with co-routines and no heap-allocated objects.