Yes, but you presume that single worker working 40h/w will charge you the same hourly rate as the one working just 15h/week. It very much depends on peoples' own perception of how much work is "normal", and if you ask them to work more then the usual norm they'll probably ask to be better paid (per hour) for extra effort. Which would make them more expensive to hire, which would lead to hiring more 15h/w workers... some sort of equilibrium would surely arise, but only for jobs that are in high demand... unqualified workers will only work more and more...

That's the trouble. From an employee's perspective, I'd like a job with less than 40 hours per week (but also be paid lesson for it). But full working hours are favourable to employers.

You're right but I wouldn't like that even as an employee (which I am). Imagine your that your team triples in size and everyone is in some kind of part-time arrangement that makes it difficult to synchronize any kind of real-time communication. Horror.

It seems easy enough to agree some kind of core - "everyone comes in 2-4pm on Wednesday and we do any meetings then" or some such. I mean, all-remote teams manage to get work done.