I know very well of 20 people atleast who use Whatsapp a lot and nobody has had an issue with battery due to Whatsapp. You can try Netguard and disable Whatsapp networking to validate your battery hypothesis, but I doubt it is true. Business features are not in the app for normal users (Whatsapp Business is a different app), and I don't even know of a single business feature. Business chats to me are like normal chats. 163 MB is below normal these days on iOS AFAIK. I think both Signal and Element have similar sizes.