Even with a battery that can be replaced using a tiny screwdriver, this still doesn’t make it DIY for probably 80-90% of smartphone users.

That's not the point. It being done in a local shop for a few bucks with no small letter text saying that "we may break your screen in half because this thing can't be repaired properly". It mentions that it should not use glue, not need solvent and only commercially available tools may be usable (or they have to be provided next to the phone).