For those who wanted to use AA miles for CX they always knew how to check for availability via QF, BA etc and would call to book; nothing stopped them from booking and using their AA miles just because you had to call. Now they can just check and book directly on AA. I don't see how or why availability gets affected because of ability to book online.

Personally, I use AS because their mileage requirements are much lower. And even if I have to call that doesn't keep me back from booking. So every time I book, does that decrease availability for others? Of course it does, no matter if I chose AS and called, or if I decided to use AA or BA or QF and booked online.