Only a rather uninformed American looking for an ancestral grievance would find anything to complain about in the term "mainland Britain", though it isn't one I'd use myself.

Uilleann pipes are not a direct descendant of the "border" pipes Pete Stewart is writing about. The border pipe has a highly conical chanter, which gives it great power and limited range, like the Highland pipe. (My cats just disappear when I get mine out). The ancestor of the uilleann pipe is the pastoral pipe - both have a much less conical chanter, which reduces volume and the ability to crossfinger chromatic notes, but (with luck) allows the chanter to overblow to the octave. The pastoral pipe itself must have ben derived from a smallpipe - these (like the French musette de cour and the Northumbrian pipe) have a chanter with near-parallel bore, but don't overblow.

Uilleann pipes are not "the most sophisticated", they're just an extreme development in one particular direction. They can't play as chromatically as Northumbrian pipes or the musette, they can't play polyphonically like a two-chanter Southern European pipe, they can't crossfinger like a Border pipe, and they can't shift pitch with a flea-hole like Hungarian pipes. There is no one kind of pipe that represents an overall optimum.