Most wristwatches provide much stronger water resistance while still being very user serviceable with a $20 watch tool kit. Whatever the phone makers are peddling are mostly excuses.

water resistance + easily battery exchange for repairs is very viable (AFIK always had been, too.)

like this law isn't about users causally replacing batteries like on very old phones

but about an repair shop easily and without risk of breaking your phone being able to replace it without only holding on your phone for idk. 10 minutes

So that you can just drop by (once they have the replacement parts) wait a moment and have a new battery.

This means in the worst case something like needing to a add a bit of additional seal/wax/glue or similar to improve sealing is very much fully viable (Id the sealing agent is generally buy able.)

It just is something you have to design in from the get to go. And it's easier to not do so at all. And maybe if you obsess if your phone is 1/10mm smaller or not that gets in your way too. And not doing so is more profitable as people will buy successor products more likely, even if just very slightly more likely.

But in general? That really isn't the problem.

Also even if it where the problem. What is better? Having a less waterproof phone, but not needing to buy a new one for another one or two years or having to buy one now?

There are multiple watches, cameras, etc., with a lot of physical buttons even, all with replaceable batteries and weather-resistant (or even better, water proof). This is a bad excuse.

Galaxy S5 worked quite well. IP67 and a removable battery.