Was in El Medano, Tenerife last week and when the wind dropped a little my buddy rented an Airush Vapor 14m from the helpful guys at the Shinn Center.
The kite performed quite well, turning nice and quickly for its size, given that it depowered so well, except for one thing: while standing on the beach with kite overhead, it just dropped out of the sky every now and then.
Now, I'm not bashing Airush here, as I really liked the kite, so I'm thinking we must have had the kite set up incorrectly. For it to fall out of the sky, I imagined we had the front/5th lines too short, but the problem was that, while riding, we had to hold the bar at quite a distance to prevent back-stalling the kite (i.e. the front lines couldn't have been too short. otherwise we'd have to pull the bar in to prevent flying to the endge of the window).
The wind was pretty marginal, but my 14m Sonic stayed overhead no problem, and would simply waft downwind before floating back up to the zenith when the breeze dropped and then increased. Also, I noticed a guy riding the 12m Vapor the next day, and he seemed to have the 5th line trimmed tight enough to flatten out the middle of the LE, while we had the 5th line pretty loose (we've not had any 5th line experience before).
I hear what you're saying about inflatables in light wind, but my 14m Sonic didn't have the same problem as the Vapor in the same wind. Yes, it started to drift back when the breeze softened, but it never fell down LE-first.