Why would a technology that makes the mind work less, have benefits for a process, that works by making the mind work hard?

You still need to calculate calculus yourself long after you could buy books where the result is written in. That supposed "paradoxon" is not even specific to electronic tools. It's just that the point of education has never been to get results, but to exercise in as much as side paths as possible and memorable while following the path to the results. The result mostly get thrown away immediately.