Hi there Bullshark1.
Question 1 - Sort of. It was tested in laboratory conditions, which in no way match living in the world. This is one area I wish Apple would redefine water resistance. Yes, it in a controlled lab setting withstood being submerged in 6 meters of water for 30 minutes. That doesn't mean if you drop your phone, for example in a pool in water up to 6 feet for up to 30 minutes, your phone will survive. It's more likely it won't. But it could. Still, Apple does not warrant liquid damage, so no one should ever purposely get their phone wet. And everyone needs to know if they do and it is damaged, it can't be repaired nor covered. I can tell you, I'm very very cautious when near water and I live on a river and live in a tropical climate where during the summer months it rains a lot. When it rains, I put my phone in a pocket to protect it from getting wet.
Question 2 - I'm not sure what you mean by diminish its surface in time. Glass doesn't actually change its composition. But there is a coating on an iPhone screen, most often referred to as Oleophobic, which reduces finger prints. This coating the more the screen is wiped or used can and does eventually wear off, meaning finger prints become more present with use. No iPhone screen ever made is immune to scratches. For that reason, every iPhone I've owned (with the exception of iPhone 6 - which was a mistake I will never make again) has been fitted with a good quality screen protector, before even turning the phone on. iPhone 12 is advertised as being made of Ceramic Shield, which Apple claims is the toughest glass they've ever put on a phone. That too can be subject to unfortunate interpretation. If you read further in Apple's page on iPhone 12, what they claim is iPhone 12's screen is 4 times less likely to shatter in a fall. That doesn't mean the screen is less likely to be scratched as many who heard the term Ceramic Shield thought. Of course this thread is about iPhone 12 Pro Screen cracking as you're well aware. And I think we've hammered that out enough, so I won't go into more detail on that.
Your welcome for the warranty. I know a lot of people are under the mistaken impression iPhone is Waterproof. You're by no means alone there.
Have a nice Sunday and if you're a dad, Happy Fathers day.