That's fine for the iPhone 5 before they got as greedy as they are in modern times. Latest generation iPhones have parts locked to the motherboard of the phone, making it alot harder for 3rd party technicians to make repairs without bricking the phone. I forget the name of the YouTuber I think it's Louis Hoffman, he goes into alot more detail on this.
But you are right in a sense, if you never break your phone, it'll last until the battery does. If you get it repaired at a 3rd party shop that's not apple certified (a really expensive certification to get, not just for upfront cash but they restrict what you're allowed to work on to keep the certification) you risk walking away with a very expensive paper weight