The American English definition of 'middle class' is bizarre and seems to include anyone who has a job and isn't homeless. The correct English meaning of the word is someone who works for themselves rather than a boss in a profession which has a guild to ensure exclusivity, e.g. doctor or lawyer. Or the owner of a small business which employs other people. It's mostly inherited upon birth and has little to do with income. For example the son of a doctor will be born middle class and will maintain that status even if he becomes a wage labourer working for an employer. After perhaps 20 years of wage labour he may then consider he has fallen into the working class. Similarly someone who wins millions on the lottery will never really be 'upper class' because they weren't born of aristocratic stock, although if they maintain their wealth while avoiding work then their children might be.
The people in Silicon Valley working for others are working class.
A doctor or barrister would be upper middle class. Working in most other jobs requiring a university education would definitely make you middle class in England.
While the American definition of "middle class" is best translated as "working class" into English English, it seems far from bizarre given it covers someone making the median income.
I don't think it's more true in the US. It's easier to get into the best universities in the US than it is in the UK. If you manage to make it, (for the most part) no one cares who your parents or grand parents were. In the UK these things matter to the point of absurdity. In the UK, the system was rigged centuries ago; here in the US our rigged system is still very much in its infancy, relatively speaking of course.
I'm pretty sure the US super elite schools (HYPS) do not cover as much of the population as the UK super elite schools (Oxbridge). I believe it's something like 1-2% for the UK and 0.4% for the US. I may misremember the components (i.e. it may be for merely elite schools, like the Russell Group or the rest of the Ivy League plus MIT and Cal Tech etc.)
Super elite term taken from Lauren Rivera's "Ivies, Extracurriculars, and Exclusion"
The people in Silicon Valley working for others are working class.