For starters, you seem to be falling into the trap of comparing the food you eat when you visit a place and go to restaurants with the food you eat at home and have to cook from available ingredients.

No. I lived in the US for the first 18 years of my life.

unless you’re talking about the local culinary tradition alone

Sort of both, of course metropolises will have a lot of immigrant cuisine, but I've found at least in continental Europe(I can't speak for the UK) that immigrants often tone down stronger flavors in restaurant food- immigrant foods I grew up with are also harder to find in Europe(Czech Republic doesn't have any Ethiopian restaurants for example, and at least the ones I went to in Vienna were not very good).

the US to doesn’t really have a local culinary tradition

That's simply untrue. Just because foods had foreign inspiration has nothing to do if its locally american food, from Chinese-American Chinese food, to American Pizza, to more traditionally american foods like chilli and gumbo(and other cajun food), american style bbq and fried chicken- etc. Tempura being based on fried foods brought by Portugese doesn't make it not Japanese.

As for the rest, in my experience all large international cities in the West

What does the west mean to you? But yeah I would agree large international cities all have immigrants, though I would argue the US has much better coverage of a variety of foods in smaller/medium sized cities. But that's also not exactly relevant. I didn't say the US as a whole is not terrible compared to large international western cities, I said compared to the rest of the world- then mentioned specifically countries(or regions) that I believe to have blander food than the US(on average).

(Even smaller places like Berlin, Amsterdam or Brussels have great variety of food in restaurants).

... Smaller places are not capital cities of major countries for the most part. And those are actually bigger than many European capital cities, and Berlin is very large.

The point I’m making is about the “average” (hence why I actually used the word “average” in my post),

You're talking about the average but listing above average cities. Compare Louisville, KY, a very average american city in terms of food, size, and income, to Prague, CZ, a capital city twice the size- there is far more variety of food available in Louisville, the only thing keeping Prague alive in terms of options is the Vietnamese immigrant community.

not the way outside the average places which are the main cities and it’s about the food people normally eat, and that doesn’t mean the restaurant trade

Again, I have found more variety and quality of produce in stores in the US- stores that I tend to go to in the US also tend to have more variety in general. But that's mostly because in the US its common to drive to larger stores, rather than going to smaller local stores- and big stores in Europe also of course have a lot of options. (Something very weird though, I was cooking chilli for my partner and I- and we could only find ground beef mixed with pork in our local grocers and not purely ground beef- but that's just a weird quirk of our area.)

which tends to be great pretty much in any large city of the World in any nation rich enough to attract people from all over the place.

From restaurants that tend to be affordable? No, I don't agree. I keep mentioning Ethiopian food just because its something important to me that would be impractical for me to cook myself, but all of Poland didn't have an Ethiopian restaurant until about a year ago. (Granted the one that opened in Warsaw now is very good.)