It's just incredibly inefficient if there's any other alternative.
Doing 4 sprints over 2 months to make a prototype in order to save 3 60 minute meetings over a week where you do a few requirements analysis/proposal review cycles.
Yeah, that would be stupid. I was thinking one order of magnitude less in terms of effort. If you can make a prototype in a day, it might deliver way more value than 3x 60 minute meetings. If you can make it in a week, where the proper implementation would take more than a month, that could still be a huge win.
I see this not as opposed, but as part of requirements analysis/review - working in the abstract, with imagination and prose and diagrams, it's too easy to make invalid assumptions without anyone realizing it.
Doing 4 sprints over 2 months to make a prototype in order to save 3 60 minute meetings over a week where you do a few requirements analysis/proposal review cycles.