[Pseudoscience-is-malarkey (OP)]

Or can this be easily debunked by pointing out that Mercury is not made of dense enough material to have once been the core of a giant gas world, and the fact that Mercury is too small and does not orbit the sun close enough?

Edit: I would delete this post if I could because this very question was asked on Reddit, Medium, and Quora and was debunked 100%. There is simply no way Mercury could be the leftover core of a hot jupiter. Its heavily battered surface, mass, diameter, weak gravity, proximity to the sun, and the fact that such a large planet in the inner solar system would have either destroyed or tossed Earth and Venus out of orbit during its migration there. So, uh, yeah...