[rognjen]

Everything you've said is true but I think we don't agree on what a proof of concept is.

I think of it as something that does the main purpose that looks entirely real (so has a domain and is responsive for example) but doesn't actually function. This can definitely be done in a similar amount of time as the XD sketch. Perhaps slightly longer but it'd look more real and therefore would be taken more seriously.

In fact its most important purpose is to save you from building something that does actually function.