The way I see it, a real intelligent person is smart and clever.
Lyle may not be as clever as Brainy, but he is still pretty damn clever. He didn't just think "hey, this floating rock could be used to make people fly", he actually built a ring that specifically exploits the rock's power, distributing it all around the wearer (otherwise they'd be "flying" by being vertically dragged by their finger) and allowing them to turn it on and off at will. At the very least, that requires a very good knowledge of physics.
The real question is not "who is smarter" nor "who is cleverer", but rather "who is smarter and cleverer overall".