The Undercover Discovery Work
Every time someone with power requests you a feature with no research to base it, don't argue with them. Instead, ask them "What's the reason for doing that? How does it improve the users' lives? What kind of business impact are you expecting?". Make sure you demonstrate your willingness to learn from them.
If the conversation doesn't flow, tell them that you want to know more about their goals with this project. Then, explore what should happen in a home-run scenario and the impact expected for the business.
In the same spirit of collaboration, build your discovery briefing with them to refine even further the related assumptions, but pivot it towards the user: • Who experiences this problem? • How does it manifest? • Why is it relevant for the user? • How will this improve their lives?
It doesn't matter whether they're just guessing or not. You have your starting point to run discovery to inform your stakeholders on translating expected business impact into solutions that users adopt and benefit from.