That’s a great point, funny enough toward the end of the discussion the PM actually said something pretty similar. That as long as it wasn’t design by committee that if other members of the team wanted to participate in the solution phase they were welcome. It’s an interesting balancing act though. The more voices you tend to get in the longer things take and if you need to make a quick delivery and a sub optimal experience is acceptable for initial testing then it might be in everyone's best interest to limit the scope to one person’s guess. Other times maybe you spend months in user research and engineering feedback to try to get it “right”. I don’t envy the life of a PM.