The saving is more from a National Insurance perspective than an income tax one as income tax is paid on dividends (and dividends come out of profit after tax)

Only first 2k of dividends is tax free, then its 7.5% within the basic earnings band, and 32.5% in the higher band.

This is from funds that have already had 19% corporation tax applied to them.

Of course anything paid as dividends doesn't attract either employees or employers National Insurance so there's a saving there, and adding a spouse or partner as a director allows the income and dividends to be split so reducing tax.

Merging National Insurance into Income Tax is one way to start addressing the issue also simplifies administration work (for companies and government) but you'd get the political issue of tax increases on pensioners savings.

Fundamentally we need to start treating earned (salary) and un-earned (interest, dividends) income the same from a tax point of view