I think that's a misunderstanding. That's a very different problem from the serde one. The compile time costs for the error handling crates is due to increase

I think that's a misunderstanding. That's a very different problem from the serde one. The compile time costs for the error handling crates is due to increase in build graph size, not due to the cost of running the error handling proc macros or the cost of compiling the code generated from them. For anything but a small project, that increase in graph size is probably not a big deal (and likely the project is already using much of the same deps). This cost does not increase as a project gets larger. serde also probably has the build graph size problem, but the bigger problem is the cost generating and compiling the generated code. This cost tends to increase as a project gets larger.