Having replaceable batteries doesn't require phones to be built exactly like they were 15 years ago. It's more about the battery being a few easy steps away from being replaced rather than the current situation where you need a bunch of exoteric tools, lots of patience and disassembling about 80% of the phone just to get there. And then requiring even more steps in a potentially dangerous process to unglue it.

And by "easy steps" I mean not necessarily something that anyone could do with their own hands in 10 seconds (like the old phones), but at least something you could do with your own tools (standard COMMON screwdrivers and so on..) at your leisure within 10 minutes without having any prior practice, just following a simple guide. They CAN design something like this that also meets all the size, weight, cost, safety and water proofness characteristics of the current phones. They just don't chose to, either for lack of incentives (our competitors won't do it, why should we?) or just because they want to profit as much as they can on the back of their customers who know no better and has no way defend from this racket.

None of that really matters since we have the technology to seal phones now, Apple just chooses not to because it makes engineering, manufacturing, and designed in obsolescence a bit easier for them.