Alumni is beatable, but you don't seem to grasp that most people are aware of that. It's not that Alumni isn't beatable, it's the odds of them winning again based on skill, experience and how many they've already won. I am not sure if there are more than two teams who have won the GST 7+ times; the amount of wins they have alone proves they have more skill than most. I would love to see Alumni lose Mixed at least once in my playtime. Not because I don't like them, but because I hate how people feel intimidated; people still feel Facebook/PC is superior to iDev, leading good players away from Mixed.
Another thing you should consider is many people from 2009+ are getting older. The real world is getting bigger and bigger for them. Alumni will retire when the real world is more important, for sure.