Part of your issue, (with Horus specifically) is that early Christians, if they knew anything about the wide-range of stories if Horus, couldn't have based Jesus on that myth is such detail anyway since (IIRC) those were buried under sand until probably the 1800s when we started digging them up.
Secondly, in your link, it was said Horus was baptised by "anup" like Jesus was by John. There is no "anup" in Egyptian mythology, unless you can show me.
So you have a few issues. (1), you'd have to verifiy that your information about Horus isn't made up itself, and (2), you would have to show the Gospel writers not only knew those details about Horus, but deliberately copied them.
I will be waiting. This is why causation matters, and is hard to prove, but it needs to be proved.