I'm a licensed plumber all you ever need to do is look at the shape of the thread to determine what makes the seal. The threads we create on steel pipes when screwed together are tapered. This means that the threads diameter increases as the thread goes which creates a joint so tight water can't force its way through. Threads that are straight usually require some sort of washer rubber etc to create a seal.

(You are)

While yes everything eventually breaks down and leaks but there are pipes I've installed like cast iron and copper that will more than likely last longer than my career and maybe even my natural life.

Shark bites and pex are very different.

I'm a licensed plumber and I would never put one behind a wall or ceiling

I think that assumption is a little high lol you need plumbing inspections to pass to grant occupancy in New builds

It's literally against code to be smaller than 3" the flange is 3" you're not allowed to EVER reduce size in sanitary drainage.