Rate of descent in autorotation is determined by the disk loading, so the heavier the rotor disk is loaded, the faster the bird comes down. The cyclic flare is the only way to slow that ROD, and this flare is also less effective at high disk loading, so the effect is doubly harmful.
In addition, the collective pitch pull at the bottom relies on rotor inertia to provide the power to cushion the touchdown, and a small rotor like those on tilt rotors has about half the inertia of a helicopter. This makes that final few feet a real problem.
I am told that the V-22 comes down like a brick in auto (the 4600 feet per minute sounds about right) and the cyclic flare is not very effective, so the auto is really a controlled crash. The V-22 is intended to come down in airplane mode, and just shed the blades on landing. Of course, its wings are highly loaded, so the touchdown speed in airplane mode should be 130 knots or so (!!)
The loading of the blades are not much of a factor here, that is more important for the maneuvering thrust capability of the rotor.