Your first paragraph is correct but your conclusion isn't. The NRL isn't in front in games watched. The measure for the number of people that watched any given program exists - its called audience reach. But it's rarely made public. If I watch an hour of both an AFL and NRL game, I count as 0.33 AFL viewers but 0.5 NRL viewers. So average audience, whilst interesting, isn't comparable when looking at viewer numbers.Yes. It you watch six hours (three games) of NRL that is counted as three people. If you watch six hours (two games) of AFL that is two people.
So, while NRL is marginally in front of games watched, AFP would be well in front of time spent watching. I.e. more ads watched, therefore higher broadcast deal.