Not to get off topic but if this guy owned his own agency he would have / should have been well aware of IRS' regs. That said, his agency went under. Not so sound nasty, but perhaps common sense and detail are not his strong suit?
Back in my freelancing days, I made a conscious effort to own the whole conversation - not to use a platform - but to do my own marketing.
As an aside, I've found it interesting to watch youtube videos made by Uber, Ubereats, Deliveroo delivery people - by scooter chargers and how they all discuss how to make more money - or to complain about changes in policies having a financial impact on them.
Upwork saw an obvious red flag and covered it's arse. I think they could have done a bit better, but the Twitter rant is foolish, at best.