A team doesn't need to create tasks during Sprint Planning. What they need to produce is a plan for turning the selected items from the Product Backlog into a potentially releasable increment.
I don't fully understand you on this part. I find the idea that tasks are just a conventional way of doing quite interesting, but I can't map it to a real life situation. Are you talking about "Proof Of Concepts" (spikes) ?
For what I've understand, the team should always be working on delivering Business Value. A plan on how to meet a PBI doesn't really add (direct) value right?
Perhaps you can give me a concrete situation. Let's say if your team have a Story like: "As a student, I can find my grades online so that I don’t have to wait until the next day to know whether I passed"
Now pretend that your team added the estimation and now they are in the second part of a Sprint Planning Meeting. Your team members are like "we have noooo idea which tasks are needed. I don't have enough domain and legacy system knowledge to know what is needed. We gave our estimations purely out of our guy feeling.
What would you do?
Also, don't forget that the Product Owner has a duty to explain the product to the team so that they can make an informed assessment.
Our PO does explain his vision and per item, functionally, very clear. He knows exactly what he wants, but again, functionally.