[remkop22]

What ever model works for a group of people producing software I'm fine with.

But as someone else said in this thread: If the question is more about who provides the estimate and less about why is there an estimate (also plenty of opinions about that in this thread) then I would say that time estimation is a integral part of an engineers job.

What makes someone an engineer is being able to provide a weighted solution towards the needs of a client or consumer. Not the best solution in the world, but the best solution for that client. If the requirements are that it should be delivered fast, you understand that the quality goes down. If the client wants high quality, it takes more time.