If you believe in the "complete" nature of the vedic school of thought, all religions are appearing from the one source anyways... so who cares what comes first?
To suggest that Vishnu is copied from christ is ridiculous... It's definitely the other way (even the word christ is derived from krista, aka krishna)
Just because you are shaivite doesn't mean vishnu doesn't exist... even your own acharayas know this.