Apple

I agree with all of your other points and I'm not trying to convince you to switch to Apple Books but you actually can airdrop books between devices! Most of the time I don't need to because I sync my whole library over icloud but occasionally I will download a single epub and then airdrop it to my ipad and it imports immediately.

I'm otherwise not picky about the rest of the things (my biggest gripe is actually poorly imported metadata! and I've finally gotten Books to show all my cover art so I can't switch now) but the Airdrop ability is a must for me and I use it a lot.