They are favouring pages that weigh less. But they don't say they are putting pages that weigh less above pages that use AMP (if they weigh more). I'm guessing

They are favouring pages that weigh less. But they don't say they are putting pages that weigh less above pages that use AMP (if they weigh more). I'm guessing it's another point on their metrics. If it weighs < X MB it's one point, if they use AMP it's another point, so those would still appear first.