That simply isn't true. An income of £80,000 puts you in the top 4% of adult earners. A salary of £100,000 is probably in the top 2 or 3%.
This was discussed extensively at the last election when Labout proposed a new tax rate for people earning over £125k https://election2019.ifs.org.uk/article/labour-s-proposed-in...
It can be more tax efficient to file tax paperwork, but I don't want to do paperwork, so I just had an umbrella employ me when somebody insisted on hiring me as a "contractor" and the umbrella handled the paperwork for which of course they keep a fee. As far as the government is concerned I just had two PAYE employers, the umbrella and my "real" job.
Having multiple employers also does not require filing taxes. One of the employers gets given a zero tax code and they tax all your pay at full rate, the other one gets a normal tax code which reflects your personal allowance and other considerations. My tax code was oscillating all over the place - but that's not a problem it's all automated.
If you love paperwork you can choose to do all the paperwork. Or if you love money and don't hate paperwork maybe you can save a few hundred quid by filing and I hope it makes you happy. I hate paperwork, and I have plenty of money. So, no, despite earning a lot of money and having worked as a contractor I preferred to stick with PAYE.
The HMRC will take a fair cut of my gross income, which is fine, and then leave me alone whereas an accountant earns money by bothering me with more paperwork.
How do you know it's fair?
Accountants don’t bother you - once a year they ask you to sign your accounts.
I'm guessing you're conflating professionals with contractors, as most high earning professionals I know do not need an accountant to file their taxes, as it's all just done on a self assessment, which is extremely straight forward, and there's little opportunity to game that system effectively.
Meanwhile contractors operating through Ltd entities (now may be hamstrung somewhat with IR35) absolutely should be leveraging an accountant to take advantage of the various ways to reduce their taxable earnings.
Yes you don't need an accountant (and I didn't say that you did) but if you want one instead of doing it yourself they just about £100 rather than I don't know how many thousand that would cost you in the US.