Actually, we don't need to question Magsayo's chance of winning the fight because he is the defending champion and sure he is the favorite to win. We should be looking more at the chances of Vargas as the challenger on beating the champion.
Remember that he is the champion, he is still undefeated, so most bettors would bet on him, now, let's go to the question, is Vargas is big treat to Magsayo, or just an ordinary challenger that can easily be beaten by the champion?
Well that is a very good way of looking at things, we all sometimes get carried away by what we can see in the statistics and everything that has to do with numbers, but it is as you say, the challenger does not lose much but the champion defender has a lot to lose, both his reputation as an athlete and the amount of money he can lose, this added to the fact that the fans support him, the fact that he loses and makes him lose money, makes many disappointed, as it was the case of Canelo, who lost and almost in many have lost the desire to see him play.
Yes you are right that mate once you are a champion it's a big responsibility to defend your belt at all times because once you already build a reputation it's hard to losses but if you loss without trying your best to defend then the crowd will slowly far from you but if you defend all of your heart and all of your best then the crowd will support you until the end of your career. If magsayo will focus in this match and trained hard for sure he will win.