Dunno what to say other than 100% of my few errors were all rotors. A brush lead broke once. The stator can fail of course but they should be super simple to check for flaws that make them do so. The only part you really can't test is the regulator, and you can even check the diode section of it.
After many years of working on cars and bikes and even the PCM controlled stuff with no formal training at all, all I can say is that you have probably just missed something since I have never seen a car or other that I eventually couldn't fix to run perfectly. When you get to the end of all work and it's still not right then obviously something was missed and it often points directly at the caliber of your work. Not trying to insult at all, I do the same to myself and how I come up with the new angle that fixes something I couldn't before. I NEVER run out of a backup or backup of the backup plan.
I do understand alts, I rebuild the PCM controlled ones on my Fords all day long, they are utter crap design and often I can resolder a simple diode contact to have one up and working again for pennies instead of buying them at $200+ apiece.
If you are pointed at stator then check it again. Reinforce your thinking that it is good or bad, there is no in between. 3 simple loops of wire, they all have a certain resistance in each and each attaches at one of its' ends to the other two to make essentially a Y with the outer loose ends giving power to the system. The Y cannot ground anywhere.