how does one measure how much work can employer extract from employee if position is 'filling a role' as opposed to having an agreement for amount of hours per day?
Another wrinkle is most workers aren't really aware of the legalities of salaried work, you'll see people making statements like the OP here about "company time" for example. Originally the arrangement was designed for people like CEOs and executives of companies where it wouldn't make sense to track hours as they had a stake in the company, but it has been expanded mostly to side step things like mandatory overtime pay.