iFixit tore open a Galaxy S9 and figured out that it was much more complex to put it back together. While the guys figured out that most of the components are modular and can be replaced independently, the outer shell of the Galaxy S9 makes it difficult to gain access to the internals. The all-glass front and rear panel increase the chances of damage to the panel while opening the unit.
I have replaced several phone screens recently, and it was not too difficult. I can't imagine trying to open up an all glass phone though; that must be difficult to not break something with the prying required to break loose the adhesive in modern phones. Manufacturers are not making it easy for us to repair our own phones... sometimes.