There are too many variables that go into battery usage to get any meaningful insight. Different apps, cpus, screen brightness/refresh rates, active radios, etc... It's an endless list. Best you can do is compare with someone you know with the same model who has similar usage patterns. Good luck.
tldr: libwebp has been patched and will eventually make its way to everyone. This is not an easy exploit and unless you're at the level of a nation state target, don't worry about it.
It might be easier to get suggestions if you go into more detail about the functionality you're looking for, whether it replicates paid features of other clients or something else altogether.
If you're going to store something on someone else's computer (Google cloud), they have every right to control what is and is not allowed on their systems. Don't like it? Use encryption, selfhost, etc...
I know these guys are too busy to do it but I would gladly pay a monthly fee for a podcast with Steve (GN), Steve (HUB), Wendell (L1) and Gordon (PCWorld).
Kobo with calibre-web sync has been great. Calibre-web github.