I’d say this was a fair assessment, as someone who eats Mexican food in the US (but wasn’t that impressed with the food in the big resort hotels in Cancun and Playa del Carmen, in Mexico) whenever I visit.
The only great mexican food I’ve had in the UK was a restaurant in Manchester, around 1990 (Manchester was once known for its authentic foreign restaurants, rather than just changing the food for the locals). It was wonderful. Never found it again when I looked.
I’ve never eaten anything close to since. While in the UK people seem to think that we like authentic foreign food, because indian curries are so popular, but in reality, we seem to be seekers of the bland for most non indian dishes. Thai food is bland (I’ve eaten in a decent UK Thai, but it closed). Mexican food is basically unspiced tortilla variations over here, priced highly too (so not a source of cheap eats). Absolutely no sign of heat in there too.
For instance Old El Paso is the main home cooking sauce/mix/tortilla provider. They produce a bland fajita mix. Except they had to make an “extra mild” version because the original one tasted of something. Anything.
Inside Europe, a lot of countries are very unadventurous cuisine wise for new immigrant food. Don’t order a curry in Belgium. Italy barely has any immigrant restaurants. Germany likes the Turkish food, but the worst curry I’ve ever eaten was in Hildesheim, near Hannover.
Yes, also immigration seemed to one direction, and the food tends to come with the immigrants. So, there’s that (fella, as they say in Fargo).
However, I’d say pretty much the main factor, which people forget, is that Spain was a fascist state for 50 odd years, when not a lot of immigrants and new ideas was welcome. Just when the rest of the world was widening its taste cuisines. So Spain will always be somewhat behind in that sense.
This wasn’t helped by the influx of british tourists in the 70-80s and the bland British food which was brought with them. Imagine the horror of that influx. Yes, most major tourist destinations were far more British than Britain… So the trauma of that after 50 years of denial. Well, would you want to be adventurous?