iPhone X battery swelling and screen lift

Unfortunately batteries can swell. It's not necessarily an issue of quality of the battery or the charging system. It's just something that happens randomly. I've had it happen with my old MacBook, but due to the design, it didn't damage anything internally but just bulged out the bottom. Apple actually offered a service replacement cheaper than a retail replacement battery.

There are ways to reduce the chances, but for one reason or another they're not available in most compact portable devices. Stuff like active cooling via fans and/or radiators. And most are packaged in thin membranes. This isn't an Apple or Samsung issue. It's not Simplo or Dynapak. It just something that happens occasionally with this particular technology.

I don't know how rare it is, but it's something that happens to some extent with pretty much any lithium-ion batteries from any supplier and used by any electronic product. Apple doesn't have any access to super special battery technology. They have specifications and buy from large battery manufacturers like Dynapak, Simplo, and Samsung-SDI. Other manufacturers have similar problems and treat them the same as Apple. If swelling happens within the warranty or extended warranty (AppleCare) period then it's a covered defect, including any additional damage to the rest of the device.

But that's what warranties are for. Warranties aren't necessarily guarantees that a device won't fail, but rather liabilities borne by the manufacturer or seller for a specific time for any failures. Once the warranty period has expired, they don't pay for repairs. They obviously have an incentive to not have to pay for warranty repairs. and there isn't some magic switch turned on to allow for a higher rate of failures once it's out of warranty.

Again - this isn't unique to Apple devices.