Do those who expect that Perez finishes higher than Button realize that they're saying that Perez is at least the equal of Hamilton, but you could very well argue then that he is better than Hamilton? Because over three years the difference between Hamilton and Button is marginal, although in two of those years Hamilton finished ahead of Button (at least this year so far Hamilton is ahead of Button).
Looking at the past three years at McLaren, I don't expect that Button will end up with a lot less points than Perez over a season.
Actually I think it's more likely that Button will end on top.