I don't think that's a valid approach. A girl once told me that she had met several very well-hung fat men who knew they didn't need to worry about being overweight because of their penis size.
She talked about one man in particular who had seduced her very quickly because somehow he had figured out she was a size queen. His dick was about ten inches long and she had been thrilled by it. "A man with a dick like that can be fat and it doesn't matter!" she told me.
On the other hand, I am quite thin--and so is my penis.
Apparently those guys had extra to spare and still be hung (they would have been even more hung if not overweight). Of course that occurs. My postings are about correlations. Surely you aren't trying to deny that putting weight on will put weight onto the pubic fatpad. Let's say a guy at standard weight for his height has a dick 8" long measured to the pubic skin, and a 1" deep fatpad (1" is about the overall average pubic fatpad thickness -of course it varies from individual to individual. In other words, his penis is actually 9" long measured to the pubic bone but is seen as 8" long because 1" is hidden in the fatpad). If he then puts on 100 pounds he may add another 1" to his pubic fatpad, give or take. In other words, his pubic fatpad will then be 2" thick and his penis will have 7" visable. He's 7" as far as his partners are concerned (and officially 7" by standard doctor measuring method) because they go by what they see. Even if he presses his pubic fatpad in some during sex it's still going to interfere somewhat with depth of penetration.
Your example can be applied to Ron Jeremy the porn star. He has actually said that he was two inches longer in his younger days. How did he lose 2" of dick? He's gained a whole bunch of weight, that's how. He had so much showing to begin with in his younger days that he's still hung even after burying 2" of dick from then by putting on so much weight, but he use to be far more hung looking than he is now. Hung guys don't tend to have as much to spare as he did.
Therefore, yes, if a guy has plenty to spare he can gain a lot of weight and still be hung, but that does not mean there is no correlation between weight and fatpad. Of course there is. Since there is a correlation, and since my posting is about increasing the odds, then it is a valid factor to be taken into consideration. Guys that are not far into the hung looking range can lose that look by putting on enough weight. That can and no doubt does occur, therefore the weight factor is valid.