Popping off the battery cover or removing the external sim tray are not the same as removing the chassis back on the phone. Go ahead and give that a try ifixit style and see what response you get regarding a warranty.
Without question there are some products where the manufacturer doesn't care about certain things. The oil filter in your car, etc. But, for the most part, warranty coverage ends if the product is unsealed or any internal component is changed. Including the PS5, LOL. It's got anti tamper stickers in several places. You can't even remove the fan to clean it. Sony is fine with the expansion bay, but absolutely nothing else. I never thought this would be a debated concept.
The size drive they use inside the console has nothing to do with anything for the consumer. Would not have changed the price they paid for the box. Sony could have used a 2280 in the PS5 also, at least it would have been replaceable and not soldered to the board. But, that wouldn't have any effect on the consumer either.
MS wanted the little hot-swappable cards for external storage and that's what they made. I guess they could always release a little adapter to allow 2280 drives to fit in the expansion slot, but that would just trigger a lot of additional testing and things like that. Seems like they wanted to simplify everything by ensuring that everyone was using the same spec drive. Sony made a different choice.