I think this argument has gone beyond studying the facts of the problem and has gone more into the emotional responses to such things. Even if the book or the errata says something, there's no reason a GM can't houserule things to be differently. The only time that the rules interpretations even mean anything is when dealing with Missions. Everything else is up for debate and can be argued until the cows come home. Personally, I try to respect other people's interpreations, not change them. I've not always been successful, but I do my best.
Personally, I felt that Mystic Adepts were potentially unbalanced with the original rules. I had a debate with a player of mine who likes to munchkin things, and he basically built a series of Mystic Adepts that would very quickly overshadow all of the other players in a group. He would start weaker, but it wouldn't take too long to compensate for the weaknesses. When I mentioned Astral Projection, he said he didn't need it to be a good mage or to be a good adept. When I asked him about his attributes, he said he was going to work on getting quickened buffs or sustaining foci for buffs. When I mentioned the skill distribution to him, he put A in his skills. His plan was to use special attribute points to max out Magic, and just buy spells later with Karma (they're only 5 karma, so they're pretty cheap). He had the whole thing mapped out and it would have eventually totally eclipsed the whole game.
His munchkin behavior aside, he had a point. Mathematically the way that Mystic Adepts were built in the original rules were pretty weak to start but would very quickly become extremely powerful, so long as one was willing to dump a lot of Karma into spells and such. So I houseruled that the Mystic Adept would have to buy their power points at 5 Karma at start instead of 2. He took the negative qualities, which gave his character more depth and flavor, and ultimately prevented him from becoming too munchkin. The houserul actually broke him out of his munchkin role, and he's become a MUCH better player as a result.
I respect everyone's views on this issue, but ultimately houseruling things will solve whatever personal problems anyone has. It helped to solve mine.