Yes, this is the standard explanation for the heavy flyers - that they were gliders. It does not hold water when critically evaluated. The logical hoops through which one must jump to support these kinds of theories are actually downright comical.
Surprisingly, we are in (partial) agreement here.
All recent evidence and analysis points to the fact that Pterosaurs, in fact, were not "gliders" but could take off on their own power (of course, all birds 'glide' when aloft to conserve energy, but I suspect that is not what you meant...
oh, and I don't think anyone who thought about it a little would describe a Pterosaur with a 40-foot wingspan, weighing 200 pounds a 'heavy flyer'.....
By the way, scientists also used to think that, based on their analysis, there was just NO WAY that a bee could manage to fly.....