I have worked in the industry for 20+ years and here are my observations - granted, I have worked in smaller companies (i.e 25-4000) and startups.
Estimates work as a means to determine the work effort for a given set of features. They are not to be used for setting schedules and deadlines by themselves. They are to be used for budgeting and cost planning. And, they are not to be done without a detailed design meeting the agreed upon requirements.
Unless your client is very rich and/or stupid or you have a large surplus of venture capital in your startup, you better be concerned with the work effort and time to have your product in a usable state. When you can tell a client that a project is going to take time X and cost Y and meet those values, you gain credibility and trust. In the digital advertising world, those with credibility and trust become the agency of record (AOR). And, the client will stick with you as their AOR until you royally screw up and fail to deliver what was promised, when promised and for the agreed upon price.
You DON'T ask a developer how long something will take - they invariably will underestimate the work effort. Instead, at least until you have measured delivery rates for your team members, you use industry standards. You can ask the developer and then compare their estimates with the actual time and effort. When their estimates start matching up, you can ask them estimate their own assigned work. It can be a good learning experience for them.
Some projects don't require estimates. We had projects that fit a template model based earlier work. We knew how long it took, on average, to fill the various fields of the template. Throw in the project management, QA and deployment components and its pretty easy to do.
When people claim Agile isn't compatible with estimates, it's probably because the team isn't concerned about documentation or planning. They tell you that the system has too many variables and they don't have time or resources to keep the design up to date. I call BS. If you can't do it, then add someone to the team who can. There are great tools for doing design work and capturing requirements at all phases of a project - use them.
Even with Agile, you should layout out a basic design or framework in the early stages of the project. Then, you can determine how long other features will take and what their dependencies are before you attempt to implement them and emptying the client's wallet. Then, you base the number of sprints based on that information. Since you are supposed to have a working product at the end of each sprint, you should be able to tell the client what features will be in each deliverable and cost. If they want to change the requirements or add new features or change functionality, you still have to plan how long those features will take and in which sprint you will deliver a product that meets those changes.