Definitely the people working on the model. It ultimately doesn’t matter what the users want because you can’t arbitrarily deliver an experience. You can only deliver what it’s possible to extract from the model, so growing the possible things the model can do well is most important.

Engineering and product are both important.

Without engineering, you don't have the capability.

Without product, you don't build something users are actually interested in.

I've seen too many engineering teams try to productize what they want, not what people not-them want, and then be flummoxed by lack of adoption.

Nothing sucks more than burning the midnight oil to nail a target... that ended up being 2m to the right of the actual target.

In my mind you could not be proving that we need product people more. They'd never say "It ultimately doesn’t matter what the users want" - they'd say "let's find a way to build what users want" not "let's grow the possible things a model can do well".

I have experience in both R&D and product. Both need different approaches to work. The goals of people working on the model will be different from product people. As mentioned by the other user, a product team can look at things produced from research and see how it can bring it to users.

If engineering/research is all mattered we would have maybe two order of magnitude more successful products or companies. Because product-market fit is a thing we don't have any successful research turning to successful product.