OBVIOUSLY, as a newbie, you haven't read the threads and contris leading up to this fight as Canelo has been absolutely HAMMERED on these boards due to this reasons you've listed above.
You think those extra couple of pounds would have allowed Canelo to develop extra skills to defeat Mayweather?
Khan absolutely deserves a lot of respect/credit for taking on Alvarez. He was moving up in weight and fighting a fight in which everyone knew he was going to get knocked out in and still went through with it. Of course the big payday was a factor here but Khan is able to make nice paydays in much more winnable fights on Showtime/HBO if he wants. He didn't need Alvarez or the risk to make good money and build a nice career but took the risk anyway. It shouldn't really be a surprise though since Khan has always fought top fighters for most of his career.