Granted, I am not nearly as we'll versed in the suttas as others here, but I've recently come across a few that seem to illustrate the Buddha as having a "This Dhamma is the complete Truth, gained through knowledge and insight. Others are mere facets of the greater jewel that is this Dhamma." I'm thinking in particular of Ud 6:4; 67–69, the Blind Men and the Elephant sutta.
The general tone, in my readings so far, seems to be one of accepting that most faiths have an element of the truth, but that there is only one Complete Dhamma.
"Change alone is eternal, perpetual, immortal." - Arthur Schopenhauer