Well when I watch the shows about this stuff, they admit that there is a lot we don't know about what exactly happened during the big bang, what was before.
Was the big bang from the big crunch? Did a previous universe exist before ours? And when our universe is done and freezes and gravity wins (if that ever happens) will the big crunch lead to another big bang over and over.
We just don't know.
So CMB does not prove anything. It actually brings up more questions than answers.
It's great we admit we don't know.
Yesterday they were talking about something Einstein thought was his biggest failure but he turned out to be right.
It is not only possible, it is absolutely certain that our understanding of the Big Bang is incomplete. Cosmic inflation is a widely accepted theory about what happened during the first fraction of a second during the Big Bang, but it is not proven.
Not even CMB has proven it DING