They keep talking about Sergio's "genetics" because he's black. So you KNOW he must have better genetics than Arnold, because we all know black guys have superior genetics for bodybuilding right? 
This despite the fact that he looks like shit in the pics you posted. Doesn't look special at all. I see no reason to think he has better genetics than Arnold.
FACT IS:
Arnold always displayed superior conditioning(genetic propensity to work harder).
Arnold always had a bigger chest(genetic). This is the consensus of the VAST majority.
Arnold had biceps that were full and peaked(genetic). Sergio's were just full...
thus, Arnold had better biceps.
Arnold was taller(genetic), making him more imposing and impressive overall.
Quads are up for debate. Personally, I think Arnolds are superior because his conditioning was on.
Sergio's 'powerlifter' thighs aren't impressive.
Sergio was a shorter man with relatively big arms, unusually small waste, consistently sup-par conditioning come contest time, and average everything else.
These are the facts...
AND
THE JUDGES AGREE WITH ME!
Yes, Sergio wasn't black. And no, we're not talking about his better genetics because he was dark- a quick look at his physique should tell you that he has a better frame for bodybuilding.
Yes, Arnold always displayed better conditioning. However, does this better work ethic indicate a genetic feature? Hell no, a personality trait such as this isn't genetically informed, it's a socially produced feature. I'm not doubting this for a second- that Arnold had a better work ethic and conditioning- however it would be incorrect to assume that that was down to genetics.
Arnold had a bigger chest, and a bigger rib cage- yes, that's genetic. Never disputed that. I wouldn't contend that Arnold had a better chest. However, I would also mention that there was absolutely nothing wrong with Sergio's.
Arnold's biceps were
not full. They were peaked. Of course we're talking relative to Sergio, not relative to someone like Franco Columbu. This is a matter of taste- again.
Quads- this comes back to conditioning, so it's hard to double cross Sergio here. You could go through the whole body and pick the body parts apart for detail- however it comes under the conditioning section. Sergio had better shaped thighs, more massive and balanced compared to his upper body. Arnold's were more detailed.
However, so are Ethiopian starving adult's. Don't forget about hamstrings- Arnold's were non-existant compared to Sergio.
Everything else, Sergio had Arnold on.
I notice that you keep returning to chest, biceps and a half-hearted examination of the thighs. This does not equal a better physique in a bodybuilding contest. It might for the chicks out there- and if you're bodybuilding for the chicks and are developing your money muslces, well fine- good for you. But bodybuilding is about more than chest and biceps.
And
Arnold himself doesn't agree with you- he has commented that Sergio deservedto beat him that day (1972).
