I think that you are not giving the person using your module any flexibility about what subroutines they are accepting from you, and you are guaranteeing that some maintainance programmer later will be staring at some code and have no (easy) way of tracking down where sub1 and sub2 are defined, let alone what they do.

If you are developing any significant amount of code, both of these limitations are bad enough to keep me from wanting to use your module.

In short, Exporter doesn't offer its flexibility for the heck of it. It offers flexibility because that flexibility when used appropriately is useful for improving developer efficiency. If you don't like trading off runtime performance for developer efficiency, then Perl is probably the wrong language for you. You would be happier with something like C or C++ that allow you to get far better performance at the cost of more up front work.

Also if you are concerned with startup time because, for instance, you are trying to speed up a web page, then you would be far, far better off to eliminate it entirely through something like mod_perl.