I'm pretty sure "healthy Shogun" was his pre-UFC form, so those arguments don't really matter.
But healthy Cain is definitely real.
I'm pretty sure Healthy Shogun was leaving his prime when he broke his arm stopping a takedown from Mark Coleman in a match that had no business even being made in the first place.
Then came the knee injuries, the failing cardio, tapping to strikes, the skateboard incident against OSP...
He was ridiculously brittle, and if I had to wager a guess, it was because he got the shit beat out of him in training by a squad of monsters.
What most people forget about the PRIDE era is that the dominant ones of the org were those who innovated and tailored their fighting style to the specific rules of PRIDE.
Wanderlei & Shogun had a system where they'd throw heat at their opponents until they panic wrestled, sprawl the takedown, and brawl all the way back up to the feet.
Takedowns were risky ventures, as it only takes one well placed knee to end a fight, thus the front headlock position became the new back mount in PRIDE.
Grapplers had to go for submissions, passes, etc... or they could lose up to 20% of their purse during the actual match.
No lengthy stalling to try to get a TD, or it could cost you, both in damage and in fines.
When PRIDE folded, these fighters had to adopt to completely different rule sets and forfeit the competitive advantages they had developed during their peak.
Many careers and legacies died with PRIDE. Some of them survived, and some thrived, but they weren't the same fighters as they were before. Adapt or die.