My mount will handle a 550D no problem. I've tested it with a 30D, with a Canon 35 - 70 zoom and it was fine.
Unfortunately to properly carry and control the weight of camera you want carry, the mount needs to be strong and there's no way to avoid a certain amount of weight and quite a high cost.
Photo Higher are the only mounts that I know uses toothed belt rather than gear drive, although I notice they now use gears on the roll axis, (but I think that's necessity of design rather than choice), and for pan on some, but not the pro mounts. From a performance point of view, belts are the route to go for smooth motion if you can.
Painful in the wallet department though!!