If this is the ownership and Engineers ask "How?", there's no one overall to connect the dots. For instance with this ownership dynamic product managers will come up with what and why, and engineers will come up with "how", but no one validates whether the whole thing is worth it considering the technical complexities involved. So scenarios where PMs come up with this and Engineers just ask "How?" there will be initiatives that take a lot of resources, while not giving enough in return.

There's no one to balance the complexity of building this vs the gains achieved.

I think best engineers would be people who also use the product and can give their own insights on this, as well as best PMs are someone who have good knowledge of the technical background and context.