Yeah, alternators seem to be a bit hit and miss in my experience and I do wonder if its climate related. I've a Golf 4 in Zuberec that has had to have an alternator (65kmiles) yet my "classic" Volvo on 210k miles still has its original (in my ownership for 20+ years) in the UK. The SK winters do punish the battery and there's the extreme blower and heated rear screen, daytime headlights etc.
I have to agree that needing a new alternator at 5 years old, really is not good.
The brakes tell a tale of a car that has either sat around for a long time not being used, so maybe the lack of use, and climate where you live have both been contributing factors in the state of these parts on such a relatively young car.
I am going to guess that while you have only shown the back of the discs the outside of the discs probably looked ok if you were to look at them through the wheels.