Writing C++ code than can outperform GC memory management is practically idiomatic at this point. It is muscle memory for people that do it for a living. There is nothing a GC can do that cannot be done as well or better in modern C++.

The real disadvantage of a GC is that it makes schedule-based optimizations difficult-to-impossible, which are a major optimization class in modern systems code. Even if it performed identically to manual memory management (which it doesn’t), the loss of scheduling control would adversely impact performance of codes that make heavy use of scheduled-based optimizations e.g. modern database kernels.