I have honestly thought about purchasing some stock from fighter breeders (please
no-one assume that I support fish fighting...) after reading some articles on how particular they are with these fish, and the standards of health applied. Fish which are 'weak' (run away/are ill/lethargic/etc) simply are not bred from at all.
It's not just two random fish thrown in a jar to fight. This is a very serious traditional sport, in which the breeder's reputations and income rely on producing -super healthy- fish. Fish rarely fight to the death - and afterwards are treated for injuries so they heal and can fight again, and breed the next generation of fighters. They don't get sick at the drop of a hat (this being my point) and will easily survive injuries which would I doubt many 'pet' bettas would at all, and heal very quickly in their little earthen jars with some IAL. The winners are 'heroes' and these are the fish which are bred from, so they pass their toughness on to the next generation. A breeder's reputation means a lot to him, so breeding weak fish would damage his pride and family name.
Winning lines are jealously guarded, I read, so 'outsiders' don't have much chance of getting hold of those fish.. but the way I see it, even a lesser version of the great fighting fish has to be tougher than than a 'regular' betta, as far as capacity for healing and resisting disease, etc, goes.
To me, this holds the same interest as keeping a wild betta, as they are so far removed from HM's and CT's as to be almost a different fish entirely (and sometimes are hybrid with wilds, but not always).