The outnumbered & thinly stretched RSA may have failed miserably in their attempt to annhilate the 28th. But one can safely doubt that the RSA failed as much as you suggest. The RSA may have been poorly deployed in the aftermath of the destruction of Nasir Oric's HQ, but they didn't 100% fail.
The UN forensic experts testified that they found at least 600 KIA of the 28th. It is unlikely that intercine fighting among the 28th killed more than that.