Bro Kisame doesn't regenerate just 'minor' attacks, there was nothing Minor about what Killer Bee did to him, the guy blew out Kisame's entire torso there were like absolutely no internal organs left his whole torso was a massive hole, and Samehada regenerated all that in an instant.
Honestly, I think Kishi realised that he made a nigh invincible character which is why he had to create the Samehada betrays Kisame plot because how the hell would he have been killed otherwise?
The guy has a giant water shark bullet that absorbs chakra instantly whilst using said chakra to grow stronger and bigger, Goodbye susano'o.
He has samehada to break him out of genjutsu, that's if the genjutsu takes in the first place considering the fact that the user's chakra has to enter the target's chakra network but how does that happen with Kisame and Samehada constantly absorbing and converting chakra?
Jutsu such as Amateresu and chidori get absorbed and fatal taijutsu or sword wounds get instantly regenerated.
Kisame is a beast wouldn't be surprised if he absorbs even Naruto's senjutsu without turning into stone.
"It was stated that Samehada absorbs chakra and "Converts" it into physical energy for Kisame" (That old guy who was watching Bee vs Kisame fight said so when he was analyzing Kisame's abilities).
I suppose a space time jutsu user could like Sasuke, Minato, and Tobi could beat him by teleporting Samehada away from him. Though considering that every jutsu uses chakra, who is to say Samehada doesn't cancel the teleportation by absorbing the chakra that the jutsu uses to function.
I think there would have been a lot of plot no jutsu or contradictory plot lines required for Kisame to actually lose a fight if Samehada didn't betray him. Kishi was smart to introduce that plot device.