My closing argument, then I'll shut up and you guys who own RV-10s can continue to say how sufficient having only an SPL is.
Some facts below are inaccurate because I don't feel like looking up the exact numbers, but for the most part true.
In a time not so long ago there was this thing called Part 103 (Which still exists today) that required zero training to fly, these planes (and I'm not sure the FAA even recognizes them as planes) had to be under something like 250 lbs and only capable of hauling the pilot around i.e. single seater. Realizing that a 250lb object capable of helping a person defy gravity was potentially dangerous, and especially if the person had no experience piloting aircraft, the FAA extended an olive branch and said "Hey guys, if you want to build a 2 seater variant to teach people to fly theses crafts, go right ahead and we wont even saddle you with onerous regulations, just get a cert from the ultralight association and you can put 2 seats in and raise the weight up to 1000lbs or so FOR TRAINING ONLY and WE MEAN IT". Well, next thing you know, a wink and a handshake later and every Tom Dick and Harry is an ultralight flight instructor "wink wink nod nod" Pretty soon they're flight instructing their wives, husbands, girlfriends, boyfriends, friends and unsuspecting strangers right into the ground or ER. So the FAA says, "We knew they'd hang themselves" so they step in and regulate every 2 seater right up to but not including a C-150, because those are already regulated. Some of the already regulated rag wing Pipers, Lubscomes and Aeroncas slide in at about the same weight as some of the "wink wink nod nod" instructional ultralights so they get covered by the new regulation too.
The FAA says to the "wink wink nod nod" instructional 2 seat ultralight crowd. "You're going to get some instruction and oversight to operate these, we'll knock the training requirments down to a little less than PPL and won't subject you to the medical regulations, as long as you haven't failed a medical, but this wink wink nod nod instructional 2 seat ultralight trainer BS is stopping".
2 seat ultralight problem solved via closing the gap between pt 103 and a Cessna 150. In other words an extremely small segment of aviation where only VERY few planes exist and only a few already regulated planes exist. A virtually non-existent market, there was ZERO market for the higher end LSA (a la Piper Sport, C-162 etc...)
Next thing you know, Ole Joe realizes his old Aeronca can now SQUEEEEEZE in to the new "fat ultralight" regulation and he can sell it to Jim who sold his 172 because he had medical problems and didn't bother to renew. Jim thinks 'I could get by with that" SOLD!!! Then, manufactures are like "Hey we could build some of these things and sell em' to the folks who can't get a medical."
There was nothing stopping people from flying or building planes that could qualify as LSA before the LSA rules were in place, Cessna coulda built the C-162 60 years ago, they didn't. There was just ZERO, NADA ZIP, ZILCH demand for it save for a few part 103 folks skirting the laws by claiming to be instructional aircraft. There is a market for a plane you can fly without a medical though, and with the boomers ageing, a potentially large market.
What the SPL is, is a niche market of aircraft that sprung from a regulation to clamp down on fat instructional ultralights not being flown for instructional purposes. A SkyCatcher isn't built as viable alternative to a larger airplane, it's built as a trainer and/or an option for a guy with $100K+ in his pocket and buys it because it's about the nicest thing he can get and fly without passing a medical, and he can't pass a medical.
One could argue that the PPL standards are "too much" of a barrier to entry into flying and that the SPL rectifies that? The FAA lowered the standards and created the Recreational Pilot cert, virtually no takers. For the most part, the barrier between SPL and PPL is non existent EXCEPT FOR THE MEDICAL requirement. If cost is the barrier between SPL and PPL, just hang it up now, over the course of flying and staying proficient , the cost and time commitment is insignificant between PPL and SPL.
If anyone here thinks I'm coming down on them for flying SPL, I apologize. It's just not appealing to me. If you can only fly SPL due to medical concerns, my heart is with you, I'm sure I'll cross that bridge one day too.
In my utopia the FAA would just drop the 3rd class medical requirement for domestic PPL privileges, my hunch is the SPL would dry up overnight if they did. That is why I think a perfectly healthy person with no issues should just get their PPL instead of settling for the loophole closing, that had zero demand until you bring the medical argument SPL license.