My take, for what it is worth!

“if somebody makes so many enemies and goes at war with ALL of them at once, such a nut would never live long” Ridiculous and implausible indeed

Michael as the main character obviously had more screen time So, we see all of his ruthless, heartless, disgusting whatever acts

I reckon pretty much every such character “isn't only a killer, but a hypocrite as well” to single out one character is apples and oranges, disproportionate comparison

None of the other characters had to contend with their insolent sister, brother's betrayal, wife's abortion etc.

If my memory serves me right, among others,

Vito killed Don Fanucci and took over his business [Granted Vito looked after the people as well unlike Fanucci] Moe Greene was made an offer no such offer to Fanucci
band leader's signature or brains on his Godson Fontane's contract release
killing of Khortum horse
went back years later and killed, a senile, one leg in the grave, Don Ciccio who was living out his last days thousands of miles away absolutely no threat to the Corleones as revenge for killing his family because same as Michael the enemies have to be wiped out
planned all the dirty work – killing of Carlo Rizzi and Moe Greene, the baptism murders – for Michael to carry out after Vito's death thus leaving a murderous legacy for Michael

Barzini was getting “impatient with being the Number Two Don” wanted to dethrone Vito and take over
Barzini, Tattaglia and Sollozzo attempted to kill Vito twice because Vito wouldn't help them with their drugs business even as Vito lay helpless in his hospital bed
killed Sonny
presumably on Barzini's orders, Fabrizio planted the car bomb to kill Michael, which ended up killing Apollonia
Barzini was going to kill Michael, the new Don Corleone

Tessio set Michael up to be killed

Roth tried to kill Michael, who was like Roth's son / successor! [could have been the entire Michael Corleone family] in the bedroom shooting
planned to kill Michael in Cuba

As regards the wives and perhaps the children too, them being “property” of the men seems to be the culture then,

Vito shut Carmela out of business too, starting with when he went into the bathroom and closed the door on her after receiving the bundle of guns from Clemenza
Carlo beat up pregnant Connie but Vito did nothing because once married the woman is deemed her husband's property
Sonny was unfaithful to his wife, Sandra which Vito was aware of
Fredo told Michael at Anthony's party “He can't control his wife”
Pentangeli dismissed / ignored his wife's concerns, when Michael was waiting for Pentangeli in Pentangeli's house
Roth's wife Marcia seemed totally ignorant of what Roth's business really was [probably hoping Roth's new business with 'Mr Paul' would bring in some money so they could eat better than Tuna sandwich!]

Roth always made money for his partners and lived like our average neighbour, harmless old man
It is just that Roth probably never had a situation like Michael burrowing into Roth's empire However when Roth needed to be ruthless, devious, murderous etc. he certainly was

Anyway in the end both Michael and Roth were beaten

“Al Pacino was absolutely terrific as Michael” indeed
I believe every actor was terrific in the portrayal of their respective characters They even looked like their characters!
All credit to Coppola for his terrific casting