Also: iPhone, iPod, and iPad batteries are replaceable; just not easily. There’s literally a connector that seperates the battery from the logic board. If they wanted to prevent you from replacing it, they’d solder them together.
That's the absolute least effective way of discouraging the practice. It's the strategy companies want you to take, but it influences companies the least. Collective action by consumers is a much better way of effecting change, including politically or legally, as they did here.
It definitely is anti-competitive to have none-removable batteries: it stops your old product from competing with your new product.
Finally, as a matter of fact, the battery in my mid 2015 iPod nano is literally soldered together, like you say, and that has stopped me from putting in a new one, like I did myself with an iPhone 3G.
They created these locked down devices. Let them feel the pain.