As I said, I too find it annoying when people like Irish names just because they're Irish, but that doesn't mean you can make a sweeping generalisation that everyone who uses one is pretentious.
I don't see why Gaelic angers you at all. I know about the history of English including the languages I mentioned, but that doesn't mean all the elements from those languages were brought into English. Look at the top names in those countries; does Alejandro make phonetic sense in English? Does Théo? You're used to these names and to the languages they come from, so maybe you don't notice the difference.
Understanding of Irish phonetics will gradually work its way into people, unless they are as close-minded as you obviously intend to be.
I don't mind you disliking Irish names, it was just the reasons you gave that I found offensive and narrow-minded.