I want you to consider instead the possibility that Waterfall came to exist, and continues to exist, for the convenience of managers: people whose methods are inherited from military and civil engineering, and who, more than anything else, need you to promise them something specific, and then deliver exactly what you promised them, when you promised you’d deliver it. There exists many a corner office whose occupant, if forced to choose, will take an absence of surprises over a substantive outcome.
I always have a hard time wrapping my mind around some of the classic user questions: What is this thing for, is it for novices or professionals, etc? I do my best to avoid these questions, because the best thing you can possibly accomplish as the maker of a tool is to build something that gets used in ways you didn’t anticipate. If you’re building a tool that gets used in exactly the ways that you wrote out on paper, you shot very low. You did something literal and obvious.
In an empowered product team, the product manager is explicitly responsible for ensuring value and viability; the designer is responsible for ensuring usability; and the tech lead is responsible for ensuring feasibility. The team does this by truly collaborating in an intense, give and take, in order to discover a solution that work for all of us.
However, in a feature team, you still (hopefully) have a designer to ensure usability, and you have engineers to ensure feasibility, but, and this is critical to understand: the value and business viability are the responsibility of the stakeholder or executive that requested the feature on the roadmap.