Realistically minimal no real help for the self-employed

The majority of high street accountancy firms wouldn’t exist if they weren’t able to persuade the self-employed that they could substantially reduce their income tax bills. Unfortunately, the way this is typically done is by ensuring that the net profits of the self-employed are as low as possible. It therefore follows that the difference between the take home pay of the self-employed and their net profits is huge. Any government scheme that uses net profits to calculate what replacement income the self-employed might get will be so inadequate the self-employed will be obliged to keep working where possible (especially the ‘trades’). A better plan would be to introduce a minimum income for all. Am I wrong?