Sarcasm points for sure, but really I do wonder if the dominance is truly dominant, as customers are only loyal until competitors arise, no?

Well, the argument is that competition gets bought up before it can rival them - ie Instagram, Whatsapp, Waze, etc.

It's a nonsense argument. Companies tried to buy Google and they didn't sell. Yahoo (among others) tried to buy Facebook and they didn't sell. There will come along a startup with a visionary founder who doesn't want to sell and they will topple one of these giants with better tech.

There have been quite a few technology IPO's over the last couple years and I'm sure many of these companies were approached by incumbents but did not sell. And some of these companies will become giant slayers.

In the US, the federal trade commission (FTC) i think has to approve those purchases, to prevent exactly what Facebook got away with.