I'm not questioning whether the dragon should be able to do it, I'm just questioning whether the large-sized synthesist with two buddies with 4d6 sneak attack who have only been unable to hit the medium-sized quadrupedal BBEG because of their 3/4s BAB, their inability to flank him, and everybody's inability to trip him should be able to do it. I'm not saying it isn't circumstantial, I'm just saying that the ability grants an otherwise-unobtainable combat maneuver to PCs which, when used properly, could potentially shift the balance of a fight, or of 5 fights, or 10. Most of the time, it's just what the label says - "awesome" - but I do think there's the potential for an unintended power boost in limited instances.
I try to avoid over-arguing a point around here, and again, you're the rules titan, SK. If you fail to consider something overpowered, than it probably isn't. I just don't consider it to be as clear-cut a case as you seem to.