fixing phones is the biggest scam ever. once you open the phone you are always going to have problems with the phone. they are not made to be opened and repaired.
Its not so much a skill issue, more so phone repair stores are the scams. they break stuff that wasn't broken in the first place and get you to come back with the that issue or say it was also broken. Source: used to work in the phone repair industry and knew people who did this on the regular and is a standard.
Depends on the model, and the manufacturers would certainly prefer you replaced it, but I've privately fixed a few phones for friends/family. Fucked up and broke the first one, but the ones after are pretty much all still running without issue.
I mind the Google crap more than I mind the Samsung stuff. At least Samsung's browser supports ad blockers since ages. That Chrome POS is just useless.