(Author of falsify here.) You are absolutely correct that the empty string isn't always the best counter-example. The goal of shrinking is to shrink to the _simplest_ possible value (this is true for all approaches to shrinking). What constitutes "simple" is very much domain specific. It would certainly be possible to write a generator that would shrink to, say, "foo", as the canonical "simplest" example of a simple string. Indeed, since we are working in a lazy language, you could (with a bit of effort) shrink to `undefined` if the other arguments are not used at all.
I agree it can be domain-specific, but I think it's more common than not that empty containers, and the number zero, are corner cases rather than typical values.
So I think it would be a decent quality-of-life improvement to make generators of the sort you suggest easily available, and have the tutorial docs use them from the start.
