I have sailed on deep fin boats. They are faster, they point higher, but they are not for me. They don't "sail better" for me. They never will. All that helm correction and tweaking? You can keep it.
I owned a Beneteau 393, a very conventional fin and spade. with a bit of careful tweaking with the sail balance, she would sail upwind without a hand on the wheel.
Sea kindliness, etc etc has nothing to with long keels, its a function of the boat design , weight and the way they are driven. Long keels existed because that was the only way the vessel could be built. The technology did not exist to attach a heavy structure to a wooden frame.
Modern fin keels ( which itself is a broad family) are proven better hydro-dynamically and computer modeling has shown that decisively. Id argue that encapsulating a keel is irrelevant in whether its a fin or not.
Yes , I like old cars and old aircraft too. But I don't persist in arguing they are better then the modern computer designed versions.
If you like full keels ( i don't know where anyone is going to buy one new these days) that fine. No doubt you like old Jaguar cars too. But accept that modern naval architects with access to infinitely more knowledge and computation modeling do actually know what they are doing.
modern boats do "sail better", they are more efficient, faster in a given wind strength, more agile, more controllable ( try surfing) and significantly stronger per llb. Modern technology allows such vessels to maintain high speeds and punch through weather, that has older designs breaking up and so they heave to. Yes this is at the extreme end of the technology, but its shows where the trend is and what its capable of.
Upto the late 60s, the concept of taking a small boat across oceans, was generally regarded as madness, undertaken by a few lunatics, some actually knighted for it. This was because the basic craft, of the day ( and hence its design) simply wasn't up the job, and required enormous maintenance and some skill to achieve these tasks. Small boat design evolved from small coastal fishing technology of the day, such technology never envisaged crossing oceans.
Today anyone in a reasonable well fitted out "plastic fantastic" can cross oceans and circumnavigate. why, primarily because the basic technology in the boat is stronger, more resilient, and efficient. Arguably the sailing skill of the owner is less, but the boat makes up for it.
A boat is a machine, technology moves forward, something designed years ago , simply cannot be better or even as good, the knowledge simply wasn't there. Boats like anything else are a product of continuous evolving
technology, there is no historical "sweet" spot.