I think coverage of the A380 often misses the point that at the time, Boeing's 747 simply had no competition, whereas all of Airbus's planes did. So Airbus pretty much had to create the A380 in order to protect its other lines from cross-subsidy by this unopposed cash-cow.
And, also missing from almost all the coverage is the fact that this worked: if the A380 is struggling, the 747 is moribund or dead. Official backlog for the A380 is ~100 planes (actual may be less), the 747's is 21. "the 747 line could be closed in the third quarter of 2019".
And I don't quite get how Boeing somehow played this better, it's not exactly that they decided not to develop a jumbo, they just already had one, whereas Airbus had a bunch of mid-size twins (in fact, the company created and was founded on the mid-size wide-body twin, the A300).
Now you can argue that both planes "were"/might be killed by the shift to smaller twins (and the shift in regulations allowing much longer ocean crossings with just two engines, heck, I recently read that they are now doing the Atlantic in 737s!), but I don't think this is necessarily so, at least not by itself.
Boeing might have been right that there wasn't space in the market for two such planes, but that's a comfortable position if you have the monopoly in this, the high-end segment of the market.
I also am not convinced that the reason given for the A380, constrained slots at major airports serving the major routes, is entirely invalid. With air travel growing the way it does, this problem is not going away, and the shift to more point to point routes may only have been a temporary reprieve.
As an example, Lufthansa recently used jumbo jets on the domestic Frankfurt / Berlin route after their competitor Air Berlin went belly up.