The problem of estimates as they exist in a "Agile" process - they force decisions to be made when the least amount of empirical data is available. Then once work starts and information starts flowing in, you can't change your estimate. The scientific method is explicitly banned! This is often by design; data-driven decisions are incompatible with management-vibe-driven decisions.

At the very least, you need to do a bit of legwork to gather data prior to giving an estimate. Call it design, call it architecture, call it research, call it proof-of-concept, I don't care. Just stop insisting that decisions be made in a vacuum of data. Real results from running code trumps everything.

To be clear, you can produce software without using the scientific method. You can build anything without a data-driven process. But you get what you pay for. The head-in-the-sand approach ignores valuable information and yields poor quality as a result - it doesn't fit the definition of engineering.