Like all law firm partnerships are pass through entities. Law firm partners have a lot of money, but its fundamentally labor income.

> Self-employed individuals who've set up an umbrella business entity aren't particularly common.

I've serviced a lot of small businesses over 35yr of IT (typically deep into operations) and I've never come across it.

Any LLCs and PLLCs (physicians, attorneys, lawyers, accountants, architects, etc.). An owner of a LLC cannot be an employee of it and therefore is pass-through.