A 10000mAh pouch battery would take up less room and provide more battery life. They are almost as cheap as 18650s too.
While using a pouch cell keeps the profile much more slim, portable, still has opportunities for really high capacity in watt hours, and allows for a more robust case design that doesn't have the structural weakness of a battery door.
And if you put the pouch cell on a set of wires with a small pluggable connector to the main PCB (and a case that can screw open/shut) it's still an item the user can replace with 5 minutes and a screwdriver if it wears out from many cycles over a period of years.
True, and you could even enclose it in a quick swap hard shell case with contacts, like the old Nokia cell phone batteries. (Those are actually still good for some uses, I have a gadget that uses them.)
We’re fortunate to live in an era of battery abundance.
Pouches can be made to have better volumetric density than cylindrical cells quite easily, which is why laptops aren't generally full of cylinder cells anymore; the challenge is just providing them enough external support/compression and swelling allowance, which can be accomplished through chassis design.