I’m curious about why you find this pattern so interesting.
Speakers are the most ridiculously draining factor, I reckon they’re even worse than brightness and/or cellular. I’ve used my iPhones to play music with speakers when I had no Bluetooth speaker at hand and battery life was worse than the one I got with light, on-screen usage (that was maybe two or three times, ever). The iPhone was in Airplane and standby mode, playing downloaded music. There’s nothing more efficient than this. Using headphones gives me a battery life of something like 50 hours. Using speakers at full volume probably gets me three (Whilst changing nothing else!!!). Where’s the point in using this usage pattern? I just don’t see one.
It’s an issue that’s so easy to circumvent (Bluetooth speakers or headphones) and so utterly draining that I never use speakers in real life. Just by plugging in headphones or using Bluetooth I reckon I’d get four times as much (or even more) battery life, so this usage pattern just kills it fast and has no benefit.