If you want flex, then you need to be in a job where flex is the agreed upon method.
My argument is that flex should be the norm. If there is no explicit reason for rigid times, they shouldn't be rigid.
Put differently: Why agree on a fixed time? Why does it matter? If the only answer is "It's normal to agree on fixed times", that's what I meant with "for the sake of normalcy".
If you're running a shop and need people to be there for customers, or you're running some on-call service or whatever, yeah, having people available for agreed-upon time frames is important. But if you're just looking to put ass in chair from 7 to 11 and 11:30 to 15:30, with no regard for whether their work gets done well in that time frame, that's just dumb.