Zelle isn't a good comparison because it's not made for things like paying employees or other businesses. It was made specifically for payments between individuals and in fact, the big banks that run Zelle could very well change the terms to specifically forbid using it for things like payroll (actually, they might already forbid it but I'm not sure).
FedNow is good for basically everything: Payments between individuals, employeers/employees, B2B, etc. More importantly, the fees are so low it might as well be considered free ($0.045/transfer) which is HUGE.