Americans totally have more knowledge and understanding of their own culture.

Irish-Americans have very little knowledge and understanding of Irish culture

They actually seem to be quite educated on the topic. Unlike yourself who seems to think that you'd have authority to speak on this issue because you have a certain passport? It's really not that wild. I moved here as a first generation immigrant about 10 years ago & I pretty much concur what they are saying. Irish and American Italians in Boston and NJ respectively feel that they have more in common with their 'home' countrymen than fellow Americans, just one example. Personally I think there's also an aspect of "oh I'm not just white, I'm actually 1/8 Irish". Mind you that's not what I think at all, why would I have a bias against you if you are white? But it's almost like I'm asked to view them as more than "white American" when people tell me that stuff after I tell them where I'm from. You can imagine what their answers typically were when I asked about whether they often go back to visit family/home or foods they cook. It's just ancestry, they have no actual ties to those lands.

One thing I will say though is that whenever I'd talk about this kind of thing is that people get weirdly defensive about it. Overall I learned just to let them say what they want to say, it's not worth my energy trying to understand their mental gymnastics as to why they're actually as Irish as I am Egyptian. They're not ready or willing to have that conversation.

I understand the cultural grouping that happens when large migrant communities form. What I don't understand is why Americans portray themselves as Dutch when coming to the Netherlands. Their customs, language, culture, and nationality are different. They're not Dutch whatsoever.

Use it to identify yourselves within the USA, that makes sense. Don't use it to claim being part of a culture that you know nothing about.