I can agree to most of the first half of this statement, but I'd have to say IMHO the second half is way off base. The housing of the "Model 20" is not as strong as a D60 nor is the ring & pinion. The brakes & bearings on the half ton axles are also smaller so if your planning big tires it's a wise move. They no longer make "full floating conversion" for a M20 that I'm aware of. Even when they did, you were transferring the load to a inadequate housing with thin tubes. In my neck of the woods I can pick up either rear axle for the same $100 bucks.
Granted I've seen a lot of guys running M20's on the the trail. I have also towed a lot of them home. I have a friend who insists on running a Dana 30 front end & a M20 rear with 38" boggers, He's blown it up spectacularly on many, many occasions. He's bought every thing "Warn" has ever made for it. Oh yeah he owns a Shop called "Off Road Unlimited" so it's a advertising thing for him. he wants every body to run that stuff cause he needs the business. He gets his repair work cheap with no sweat off his brow. He also brings a trailer when he's wheeling. BTW "Warn" has stopped warranting his "lifetime guarantee"axles.
I think a lot of differences opinions come from different terrain. I know you can do a lot to fineness you way through the rocks & trails in some places. IMHO the deep black gumbo mud of the south can be a great equalizer, yes skill helps. But wheel speed & momentum get you through. Sometimes you just have to stand on the loud petal & let her sing.
Give me the 60's.
Like I always say "Opinions are like

holes, everybody has one. That's mine.