I think you are confusing "generic code" (which is a pretty generic term) with "Generics", which has a somewhat more defined meaning in programming languages.

I think you are confusing "generic code" (which is a pretty generic term) with "Generics", which has a somewhat more defined meaning in programming languages. We could agree that the latter can be implemented relatively efficiently (given a few concrete examples to clarify what that means). But that does not mean that their use, or more generally, the use of generic code, is always the best and most efficient to do. It is not, by far.