1. Extraordinary claims require extraordinary evidence. In the absence of extraordinary evidence there's excellent reason to be skeptical about the claims.
2. There is not extraordinary evidence for any of the divine/miraculous stuff in the NT documents.
3. Therefore (from 1 and 2), there's excellent reason to be skeptical about those extraordinary claims.
4. Where testimony/documents combine both mundane and extraordinary claims, and there's excellent reason to be skeptical about the extraordinary claims, then there's pretty good reason to be skeptical even about the mundane claims, at least until we possess some pretty good independent evidence of their truth (as illustrated by the Bert case*).
5. The NT docs combine extraordinary and mundane claims about Jesus.
6. There's no pretty good independent evidence for even the mundane claims about Jesus (such as that he existed)
7. Therefore (from 3, 4, 5, and 6), there's pretty good reason to be skeptical about whether Jesus existed.
* The Bert case: if my friends say a stranger called Bert visited them last night, I'll rightly take their word for it. But if they say Bert did amazing miracles in their front room before leaving - turning the sofa into a donkey, dying and then coming back to life, etc. - well then their claim that these things happened is now no longer nearly good enough evidence even for the claim that any such person as Bert exists, let alone that he did any of the things they claim.