> pay themselves through dividends (which have a much lower tax rate), which is now (highly controversially) illegal
What on earth are you talking about... taking out dividends is not illegal, even for individual company owners. IR35 is about HMRC forcing self employed people to apply payroll taxes as if they were employed. Again, nothing to do with dividends.
Ordinary self-employed people and sole traders pay nearly the same tax rates as employed people (National Insurance, a strange disguised tax, is at a different rate), but have many fewer rights, eg. no right to paid time off or sick pay.
The question in this case is whether Uber drivers are self-employed or not. Not as it turns out.