Or maybe the Knaufs just thought that The Mandarin should be an awesome manipulator, and choose to give the rings a power-level that would supplement that without drowning it out or rendering it irrelevent? You can't really present him as a brilliant manipulator if the rings are so cosmically powerful that he doesn't actually need to manipulate anyone.

It's not a coincidence that Fraction's Mandarin has a more powerful mind-ring but Mandarin himself seems dumber. It's a natural push-pull that happens one the result of the other.