"Take this scenario for example, you have a married couple working alone as joint directors of the company. Both genuinely put 40hrs a week work in with one being the main fee-earner and the other being the behind-the-scenes person doing everything from accounts to phone answering and everything else that keeps a small company running"
There are lots of businesses like this - plumbers, vets etc - where there is a signficant input from both parties, and it would be hard on them if their respective contributions were not recognised. And if there was no partner the person concerned would have to employ someone as a receptionist/admin/bookkeeper for a significant number of hours for the business to operate.
But there are plenty more where one (usually he) is working on a contract basis for weeks or months at a time and the input from the other party is minimal. Their income splitting may be legal, but it puts two fingers up to the revenue, people like the ones you cited and those on PAYE who (school headteachers for example) probably get just the same input from their spouses, but unpaid.I suspect that on this subject those who make the most noise will be those least deserving of sympathy.