IMPO and FWIW;
The FAA took the EU regs and copied them with a small bit of tweeking. Thus the weird 1320lb. limit.
It was meant to rein in the "Fat Ultralight" community and give them an out to become legal...
They never wanted the SP rule to allow old pilots to continue to fly; as above, it was to get the Rotund Ultralight pilots to sign on! (Thus the stupid "If your Medical has been denied..." clause).
My beef with the SP rules is purely preformance oriented; with the stall parameters dictating wing planform (size/drag), the desire for the highest speed allowed and the lack of Energy (weight) in the airframes you set a combination up where the loss of the thrust provider (engine) results in the IMMEDIATE reduction of airspeed due to NO kenitic energy in the airframe...
This is a moot point in the older Cubs and Aeronca's...they had light airframes coupled to wings that would regain function if you reduced the AOA only a few degrees. But they were not, of course, as fast.
In the several newer LS airplanes I have flown I have found that, using the old "engine quit...S*IT, one Mississippi, two Mississippi rule the airspeed was so far gone so fast that the recovery mandated a deep nose down pitch to get the speed back up. Not a prob for the old Fighter Pilot but maybe above the SP rookie.
Raising the weights to include the C-150 and others that fall into the same general weight/top speed/ landing speed would increase the safety of the SP rule IMPO.
As noted above, these are only my opinions.
I would love to see an article in the mag that compared the old and new SP airplanes as it pertains to the loss of engine perfomance senerios.
One of the new SP airplanes I've flown would not make the runway if the engine quit (using the 3-mississippi count) on the base leg at 1000 feet and 1/4 mile from the threshold.
JNPO and YMMV