That would probably work fine for a majority of cases, where the shell script for environment setup tends to be pretty simple and explicit. It's a good-enough solution when you know enough about the shell script to trust that it will work.

But I can easily imagine (and have seen) examples where the value assigned to a relevant exported variable refers to some other shell variable that was set previously in the same file (and not necessarily exported), or is the output of some back-ticked command, or other arcane cleverness. For shell scripts like that, you really don't want this approach.