Building an MVP means getting something in front of customers as soon as possible, in order to test your product works for customers and change it if you're wrong. The entire point of an MVP is to give you as much time to change things as possible.
Everything you do prior to putting your product in front of someone might be wrong. The only validation that counts is the customer handing you their money. The longer you spend building before getting something out there the more expensive any mistakes might be. Consequently, making an MVP and only building the absolute minimum viable solution to a problem, give you as much correction time as possible.
I'd much rather work within an organisation that has a clear vision about the problem they're trying to solve with flexibility around how it is to be solved
We all would. The question is about how the org goes about getting clarity about the problem. If they think they fully understand it without talking to customers or putting something in front of customers in order to give the customer something to talk about, run the hell away. Those discussions will happen as soon as the customer sees something. If you've built a full product that you think is ideal, and then the customer doesn't agree, then you either lose the customer or you have to do a ton of work to change the product. Those are expensive mistakes that kill a startup. Having those conversations as early as possible is how you avoid that cost.