That's not agile, that's waterfall. With my team, I usually have just 2 or 3 "stories" that are taken up during a sprint. The rest is up to the development team. Works quite well. No one's asking to create dozens of tasks. A rough outline of what we're trying achieve combined with a high-level overview of what we think would need to be done is usually enough to get started in a sprint. If we fail, we fail, no one gets mad. That's agile if you ask me.