I do think the cumbersomeness goes up the shorter or smaller the rider and the taller the wheels. It is just the proportions. That doesn't mean you can't ride a 29er if you are Napoleon.
The only time I worry about the 29er tossablity is when I have hair pin turns in switchbacks. They are tough to maneuver and I think it is due to the larger wheelbase.
And that's a respectable height. Just like my weight in my license - nice and slim!
G