"packaged slightly differently" has to mean "packaged durably enough to protect the bare battery from damage".
By the very nature of the design constraint, a removable battery will take up more space inside a device than the same chemistry packaged without the protective case, springs to hold the contacts in place, and so on.
That means by eschewing it, you can take your pick among: a thinner phone, more components, or a larger battery. There's no way around this.
> That means by eschewing it, you can take your pick among: a thinner phone, more components, or a larger battery. There's no way around this.
That's making a lot of unstated assumptions. To start with, that the battery needed to consume all available space. The width and length of the phone are determined by the size of the screen, and a certain minimum depth is required to prevent this:
So then you have the dimensions of the phone already dictated by concerns other than the battery. At that point you could still use all of the available space for a battery, but if that's more battery capacity than you actually need, it makes the phone heavier. So you could very well already have some unused space inside the phone and not have any trade off with thickness at all, and in practice this is true for several phones that nonetheless have epoxied batteries.
Moreover, even if the trade off you're describing exists for a given phone, that doesn't prove it's significant. Do we have to destroy the environment over a fraction of a millimeter?
By the very nature of the design constraint, a removable battery will take up more space inside a device than the same chemistry packaged without the protective case, springs to hold the contacts in place, and so on.
That means by eschewing it, you can take your pick among: a thinner phone, more components, or a larger battery. There's no way around this.