It's got nothing to do with mediocre white men -
The UK is 81% white.
The UK has had mass immigration since the 1950s from its former colonies (India, Pakistan, Jamaica, Hong Kong etc)
The first generation immigrants opened takeaways, restaurants, newsagents (Indians, Chinese, Pakistanis etc). Jamaicans tended to do manual labour jobs.
Those first generation Indian/Chinese immigrants placed high emphasis on education, so the second generation became Doctors, Lawyers, Pharmacists etc. Jobs that don't require a network, just educaiton and hard work.
That is why the majority of the top C-level roles in the UK are held by white men. Because whites are 82% of the population and the third/fourth generation immigrant talent pool isn't there in high numbers to really be noticeable at the c-level. (Although arguably the early 40s Indian PM is an example of a second generation immigrant who has made it to the top)
The DEI religion says that if blacks are x % of the population then x % of CEO's should be black as well, or if gays are Y % then Y % of CEOs should be gay etc etc etc.
This just isn't a reliable target to aim at.
Factor in the women have different interests etc and you realise that the foundations of DIE are built on sand.