A Mary-Sue is a character who is overpushed, hardly loses, and is pretty much the center of the show. It doesn't even HAVE to be an original CAW. It just usually is, since they tend to represent the feds owner, and friends of the owners.
To say you cannot push an original CAW without it being a Mary-Sue is completely ludicrous. In fact, the number of original CAWs pushed WITHOUT them being Mary-Sues far outnumbers the pushes where the CAW ends up being one.
Mary-Sues are generally a sign of poor booking and a swollen ego, and effectively causes whichever fed the character is featured as a Sue in to be an endless cycle of them winning World titles.