Exactly this. the AMP badge is a visual indicator that says "we're not going to waste time your time with a slow loading webpage, so click this link over one that doesn't have the AMP badge", which incentivizes faster webpages in a way that wasn't available previously.
most clicks go to sites that are on the top of the search results, therefore prioritizing placement due to pageloading speed should be enough of an incentive to most sites. The AMP badge pretends to be an incentive in this way, but the purpose is to extend google lock in.
