Whenever I've used scrum, the developers set the estimate and task breakdowns. We even had the developer _doing_ the work provide the estimate. It's not really fair to have someone else estimate your work, it doesn't breed commitment either. We did sanity check things - sometimes an estimate would seem big and everyone else would ask why. The answer was either we had missed something (typically), or (rarely) the estimator misunderstood the task and thought it was something bigger.
At the end of each sprint/cycle we shared estimate vs actual effort, to improve our ability to make a good estimate and set an overall velocity.
On my first Scrum/Agile project, there were complaints of overwork the first sprint. Then I pointed out that we were the ones setting our own estimates, setting the pace and causing our own problems.
After that, the estimates got reasonable. We stopped playing "Name that Tune" with our estimates and the project settled down.
At the end of each sprint/cycle we shared estimate vs actual effort, to improve our ability to make a good estimate and set an overall velocity.
On my first Scrum/Agile project, there were complaints of overwork the first sprint. Then I pointed out that we were the ones setting our own estimates, setting the pace and causing our own problems.
After that, the estimates got reasonable. We stopped playing "Name that Tune" with our estimates and the project settled down.