I have no doubt that tank tests show this type of keel to sail well, but tank tests dont ask the question of how you get a fouled anchor rode off one when you are abeam to a strong wind and sea on a dark night. Numbers and math dont answer that question, and a lot more practical questions about actually using the boat..
Skinny keels fold over, regardless of what you put inside. Perhaps these boats are designed to the standard plastic boat standards, where they are simply expected to break up if they hit anything.
Brent you always seem to be worried about the things that can be engineered or designed around. Solving these issue does to take some additional care, but they are not all that hard to solve. If you are really worried about anchor rodes fouling the aft end of your bulb keel, but you want the sailing boostg that comes from a bulb, you simply run a cable from the very lower aft edge of the bulb to a spot on the hull well aft of the bulb to keel rodes out of there.
Engineering a skinny keel and its connection does require careful engineering, but the forces are well known, and it is a far easier engineering problem than designing something like a high rise building, which qualified professionals design routinely and which very rarely fail.
My first boat was a Pipe Dream designed by Francis Kinny and tank tested inthe Davidson lab in New York, the tank where all the US Americas cup boats were tested. She had a short keel with rudder attached. With zero sailing expereince, I looked at the rudder and thought " Maybe a rudder on a skeg six feet further aft would be better." Then I thought " Gee, I have no expereince so I beter do what the designer drew." Off the wind the boat was almost uncontrolable in strong winds,an absoluite abortion of a design screwup, so when I got to New Zealand, I replaced the rudder with a separate rudder six feet further aft on a skeg, just as I had originally thought, with zero experience.. The improvement was huge. That completely blew my confidence in the infalibility of world reknown "Experts."
Einstein said "Wisdom doesn't come from studying , Wisdom comes form showing up for life."
Your story about the 'Pipe Dream' is a good one. It shows how over time designers have learned to improve designs. Pipe Dream was optimized for a specific racing rule. Kinney had come into the profession when racing rules still restricted the use of separate rudders and so the design followed the 'traditional solution' of its day.
But around the time that 'Pipe dream' was being designed, designers began to experiment seriously with separating the rudder from the keel in one form or another. By the time that you owned your 'Pipe dream', it was pretty common knowledge that splitting the rudder from the trailing edge of the keel improved handling and lightened steering loads.
So what was radical in Kinney day, became a reasonably well accepted norm by the time you decided to modify your boat.
Even then designers were still learning how to design fin keel-spade rudder boats, and so these early fin keel boats had a mediocre reputation.
It hard to predict what radical idea will become the next norm. But your Angus Primrose story shows how an early experiment in boat design does not always tell the whole story. Angus Primrose's boat actually broached and pitch poled. He was known for designing boats which were lightly ballasted and which had a flaring bow with chine below the deck and a lot of buoyancy near the deck line. The version of the story that I read said that they punched that bow into to the back of a wave, and wiped out, getting rolled by the next wave. It was not about reducing beam, but about shaping his boats better.
Angus Primrose, while crossing the Atlantic in one of his very beamy designs was capsized, and was dismayed at how long she took to right herself. He later did some calculations and found that even a slight reduction in beam made a huge improvement in ultimate stability.
Again, boats staying capsized was never a problem, before excessive beam became the norm.
A beach ball with a high CG and a tiny ballast ratio has a very high ultimate stability. A wide raft with a very high ballast ratio and low CG will have a very poor ultimate stabilty. Thousands of pounds of buoyancy in a wheelhouse will be the equivalent of adding far more weight in the keel, in the inverted position, when it comes to ultimate stability. The more the midships section resembles a beach ball (Trunk cabin with high camber) the higher it's ultimate stability.
But like many radical experiments, even the beamy boat world is making progress in dealing with its inherent deficiencies. When you look at the cruising versions of these beamy boats, they often have a lot of freeboard and high deck structures, which serve to destabilize the boat in the inverted position.
If you look at this moment curve for a Malo 40, which is not terribly radical adaptation of the beamier hull forms, two things seems obvious, first it has a positive stability to 130 degrees, and second it has virtually no negative stability when inverted to 180 degrees. I have seen a plot of a much beamier and more radical design which had positive stability to a bit over 140 degrees and achieved maximum righting moment at around 110 degrees. What I did not like about that plot was the very steep drop in stability between 110 degrees and 140 degrees which could catch a skipper unawares.