You're right and wrong. People buy iphones despite the cost and lack of user serviceable battery.
They are a luxury item and a way to signal status. If people stopped buying iphones due to battery life then Apple may change. But Apple has a strong brand and the status of the item is important to people so they act against their own interests and pay lots of cash rather than use a $100 dollar android that's 90% as good.
Batteries aren't a feature to most people.
Also there's lots to be said about the scope of what most 'phones' do these days. The batteries are powering serious computers rather than just phones.
This comment has a pet-peeve of mine, which is using the word "efficient" where it's unclear what the cost and benefit are. Efficiency is just cost per benefit, so it's not a very meaningful word if you don't know what the cost and benefit are.
I don't think you're wrong, I just am not entirely clear on what claim you're making. I'll venture based on context that the cost you're talking about is either electrical charge or time, but it's very unclear what benefit you're talking about.
Batteries aren't a feature to most people.
Also there's lots to be said about the scope of what most 'phones' do these days. The batteries are powering serious computers rather than just phones.