Right now, Apple pays more per stream either because they may have more users in richer countries (Indian users don't pay $10/month), users who listen to less music, maybe older users (fewer students on student plans) and because they have no free tier.
So: the "AM has higher royalty payouts" is objectively a false Apple marketing point, because it's zero-sum. It's a pure accounting gimmick. Royalty payouts are pro-rata; there's no such thing as "Spotify's chosen royalty payout". For Spotify to get as high as Apple's, they'd need to make discoverability terrible (fewer hours listened per month = fewer streams = higher payouts per stream), get rid of their free tier, etc. They can't just "decide to increase payouts" because that's 52% of revenues, same as Apple Music, by contract.