The point is this: pain is an evolved mechanism to influence the behaviour of an organism. And for that reason, different parts of the body are innervated differently depending on their importance, how they’re used etc.
It makes perfect sense that we can tolerate a lot of blunt trauma and cuts to our limbs because such minor injury would be common, and usually of no long-term consequence. OTOH it makes sense that strikes to the gonads should hurt like hell because that means we take extra care to protect that area.
Now, there are some things that don’t fit the model so well: e.g. tooth ache (bearing in mind that, again, pain and touch sensitivity are not coupled) and headaches.
But the general idea of why pain exists is not seriously disputed. In fact, I’m not aware of any alternative theories. So it’s just a matter of trying to explain the one or two exceptions.
Well we are in agreement really. For whatever reason we have external testicles sensitivity is one of the ways to protect them as a dynamic process as opposed to something like a hard shell.