That was actually what Yoshi P. said, not me. I'd have to find a link, but he said during what I believe was an interview with Famitsu that they are going to rebalance AST, but they don't want it to overpower WHM or SCH and make them irrelevant, or make them seem like a worse choice. I didn't play FFXI, but I do recall reading quite a lot about one particular class being so outdone by all the others that players who chose it would be kicked from parties without a moment's notice. Perhaps they're trying to avoid that scenario?
That being said, as I mentioned in my first post, I want to see AST buffed. I really enjoy the class. I only became a MCH because I was excited for it for so long and loved the idea, but I was always a healer before that. As Blood-Aki and RichardButte said, it's very easy for AST to become preferable to the other two healer classes and cause people to favor seeing them, similar to how a lot of parties I was in didn't want to see a Warrior at all.