It's been great for the poor and middle class. Tickets are cheap, before taxes and regulatory charges. Go to Europe and you see what competition can truly bring: <$50 tickets.
And the same for San Francisco: https://www.google.com/travel/explore?tfs=CBwQAxoQKABqDAgDEg...
Based on these I think airfare in the US looks better, especially considering the longer distances. Barcelona-London is the same price as San Francisco-Denver but 75% as far for example.
Your data is, more or less "if you ignore the budget airlines, there are few cheap flights from Barcelona", which is true, but not particularly useful. Dublin<>Barcelona, say, tends to be 25eur each way when there's not much demand, including taxes and charges (though you'll pay extra if you want to take _bags_).
EDIT: Ah, I found the problem (I suspect this is a bug in Google's flight thing). They had carry-on bags set to 1. If you set it to 0 it shows flights (mostly Ryanair) to almost everywhere in Europe. It may be getting tripped up by Ryanair's wonky treatment of carry-on bags (you can add 'priority boarding', which gets you a carry-on, as an extra fairly cheaply, but if you want it as a headline feature it comes bundled with a bunch of other stuff).
Even with this option off, though, it's still not showing easyJet.
"Basic economy" as a category is only about ten years old, and most people don't fly much.