When IR35 was first introduced dividends weren't taxed the same way and it really was a big tax advantage to work through a Ltd. That was arguably a reasonable situation if you really were running your own business with your own costs and risks as well. However it was definitely exploitable by people whose clients were really employers offering them the same perks as permanent employees anyway.
But that hasn't been the situation for quite a few years now so the financial arguments to "justify" IR35 don't really make much sense any more.
About 5 years ago, the BBC started clamping down on star presenters who were employed through private companies. Previously they were encouraging it; if you asked for a pay rise, they'd suggest you'd be better off setting up a company.
But that hasn't been the situation for quite a few years now so the financial arguments to "justify" IR35 don't really make much sense any more.