Debian's which hunt

Well, that's true, someone might want to do that. And one way they could do that is building GNU which themselves, dumping it into a private directory, and running the ball-of-mud with a suitably modified PATH. Obviously for those needing to do this, it would be more work that way. The project has to weigh up the likelyhood of Debian users needing to do this versus the costs to the project and all other users in terms of complexity, confusion, likelyhood of bugs, etc.