I was an Android dev pre-5.0 and believe me, having lived through the s*tshow that was push notifications at the time, there's no way it would've worked any other way. Google's own SDKs were garbage and as with everything else they kept releasing new incompatible rebranded versions annually. Last I checked, the Firebase console for managing push notification subscriptions was still one of the worst SPAs I've come across.
You'd expect a thriving ecosystem of dedicated push notification providers to pop up and outcompete Google, but all of the 3rd party offerings were even worse, in terms of battery life, UX, reliability and even pricing.
It's unfortunate, but no developer cares about your battery life, because no user is going to switch away from using their app solely because of crappy power usage, so Google had to do exactly what they did.
Maybe in a decade or two, with new battery technologies, there won't be a physical limitation and this situation would play out differently.