> I need 1 agent that successfully solves the most important problem.

If you only have that one problem, that is a reasonable criticism, but you may have 10 different problems and want to focus on the important one while the smaller stuff is AIed away.

> I don't understand how you can generate requirements quicky enough to have 10 parallel agents chewing away at meaningful work.

I am generally happy with the assumptions it makes when given few requirements? In a lot of cases I just need a feature and the specifics are fairly open or very obvious given the context.

For example, I am adding MFA options to one project. As I already have MFA for another portal on it, I just told Claude to add MFA options for all users. Single sentence with no details. Result seems perfectly servicable, if in need of some CSS changes.

Exactly. And if that problem is complex, your first step should be to plan how to sub-divide it anyway. So just ask Claude to map out interdependencies for tasks to look for opportunities to paralellise.