Earlier quoted context omitted.
But, as a developer, it's soul-wrenching and just feels wrong to try to sell something before something proper has even been made. This has been my biggest struggle.
I think it's worth pointing out that in order to "sell" to investors (as opposed to customers), having the product (and the customers!) ready actually is very important. So the proper sequence is: 1. Sell. 2. Build. 3. Pitch to investors. 4. Repeat with more resources. Inexperienced non-technical founders sometimes get the steps 1-3 backwards.
I'm curious about 1 before 2. Any attempt I've made in the past to understand market interest without having something that people can actually touch has always been really squishy. People aren't that interested to talk, when you do they always say something like 'well, sure, I guess that sounds interesting'. People that seem really interested usually don't have enough bandwidth for a beta product evaluation, even though they will say they are really excited and want to help. Often, product uptake comes from an unexpected direction/vertical, just by accident.
So while in principle getting customer-based design information up front is ideal, in practice it seems like you don't get that much no matter how much you try.
Maybe you're suggesting iterating on 1 and 2 until you feel like you have a solid case for 3?