Unfortunately your anecdotal evidence doesn't change history. My experience has been very mixed bag. Some have been despicable bastards and some, as you said, have gone above and beyond. But their history, and government inquiries confirming institutional racism etc cements them still in the bastard category.

I do believe they're improving, the force isn't just 6ft+ white, straight, cis, British men any more. It's diverse enough that homophobia, racism, etc are challenged and not tolerated like they once were, but it still happens. They're still not good enough to throw off the badge of ACAB.

A middle class white lady in the US would probably concur regarding her own police experiences

It's a slogan used as a protest statement, particularly within anti-establishment and anti-police movements. The acronym has a long history, particularly within subcultures like punk, skinheads, and football hooligans. It's also associated with anarchist and anti-authoritarian ideologies.

It also originated in England.

America is not nearly based enough for Americans to "constantly say" that, unfortunately.