To be honest I never viewed American culture as anything but British culture with quirks. Or British-German culture
I'm just going to step out while the British forumites yell at you.
For example if you were a melting pot, you would use not English but some mix of various languages forming a new one.
English is heavy on loanwords. If you kept America isolated from the rest of the world for a couple hundred more years you probably would get a new language. This isn't even getting into Spanish, which is (as I recall) at 10% spread in the US. There's a growing culture of bilingualism in the Southwestern states. You also have things like Cajun French in Louisiana, Gullah in the Carolina coasts, and AAVE is arguably divergent enough from American English to be a dialect.
Or at least your English would have hundreds of words not understandable in England.
Well, given that this is exactly the case (you call flip-flops
thongs, Britain?
Thongs?!)...
USA is an assimilation pot.
It's not a binary value. You can have multicultural assimilation, though it is rarer than destructive assimilation. Personally, I think that the way we do it is genuinely the best way to go about it. European multiculturalism has turned the very concept into a snarl word. Trying to maintain cultures in separation from one another like its done there is inherently conflict-raising. It promotes lack of understanding and unending cultural clash. You can't have one society and one law unless you have a common link, but that doesn't mean you have to destroy other people's cultures and force them to be the same as you, nor is it racism to expect migrants to make reasonable changes to get along with society at large. Such a xenocentrist narrative has so far not given much in the way of results. It enriches both host and migrant cultures to accept one another and discard malignant elements from both to achieve a greater result.