It's not as hard as you think it is. Apple is indeed massively over complicating the process.
1. A machine to melt the glue holding the battery in place
2. A machine to apply even pressure to the new battery to ensure it’s properly adhered
3. A machine to apply heat and even pressure to the entire phone to properly give the phone with a watertight seal.
That seems like exactly what I’d expect has to happen to repair the phone back to original spec. I’m actually impressed that Apple gives this out to consumers to use.
It would be awesome if Apple also offered a lower cost model with an easily replaceable battery (like an old Android), more easily repairable, and not necessarily water proof. But, if there really was a market for that, some Android manufacturer would have something for it. Maybe there is one and I haven't looked.
Adhering the battery is the same - just press in place.
Heat is only needed for opening/closing the phone.
But normally (and if done correctly) it is watertight and opens +- the same.
Moreover, they changed my speaker for free, because it was defective or damaged. I didn’t know that. I only learned after getting my phone with service summary report.
As a result, I now recommend AppleCare replacement over any repair, if the water resistance is important to you.
The thing is that even if you screw this up, it will probably look OK for quite some time without being really water tight.