So how is the popular description of anybody "inventing" the aeroplane reasonably justified?
Absolutely. As it happens, I am reading Samuel Smiles, the 19th c. engineering historian, at the moment, and his constant theme is that inventions are the product of the cumulative progress of a lot of people.
But this doesn't mean we should deny the contributions of the Wrights who, as it happened, after a lot of work themselves and having studied the work of others, were the first to get it together. Was their aeroplane practical? Not by our standards, but it was more practical than anything else in 1903. And perhaps anyone who thinks catapult launch invalidates their claim should explain to a group of naval aviators that what they do isn't really flying, most of the time.