As someone who spent half his life in the world of (physical) product design: to me this sounds incredibly contradictory.

A "strong product vision" is a bad thing when you are "iterating to find product market fit", because most people tend to be unable to kill their darlings and do what is needed to achieve said market fit.

If your "strong product vision" is really as strong as you believe, it should already contain an idea which market and target group is ideal — or if it is a really genius idea, this won't even be necessary because it will create it's own market.

Perhaps it's a vision of e.g. technology which could be applied in many different verticals? I can see the founders having a clear product idea but having to find its specific applications on the market... E.g. let's say you make a database and then you begin looking for companies that need your specific favor of database; then there could be customization for specific customer needs too.

This made me scratch my head too. I see so many startups come up with an idea/product and then try to make it fit in the market. That is completely backwards; you need to find a problem that the market has and create a product that solves that.

depends on how you understand vision i guess.

imo vision is “how is your customers world going to change as a result of using your product?” not “this is precisely what the product will look like”.