How do you validate that your roadmap priorities are right?

We do quarterly roadmap planning and every quarter I feel like we're guessing. We have a backlog of ~200 feature requests, we run user interviews, we do NPS surveys — but I still can't shake the feeling that we're building the wrong things. Specifically: how do you balance vocal minority feedback vs. silent majority behavior? How do you know if a feature request is coming from 3 loud customers or represents something 80% of users want? I've heard people talk about using Reddit for market research but never seen a concrete workflow.