Was Jesus a Solar Diety?

[Thomas]

This mostly comes from the fact that prior to accepting Jesus, Paul was a Mithraic priest.

That would seem highly unlikely, and a claim I have personally never seen made. Can you demonstrate any evidence in support?

Many have suggested that Jesus was a fictional character he has created to try to merge Mithraism with his ancestral religion of Judaism.

Many? I think you're prone to exageration here. Mind you, this is no more ridiculous than many other claims in circulation.

... even the concept of trinity is actually founded on ideas that already existed elsewhere - Bhagwan/Son, Brahman/Father, and Paramatma/Holy Spirit is an obvious correlation.

Whilst there are indeed many triunes (as one would expect, the Cosmos is Trinity-shaped, after all), the correspondences are largely superficial. Once you get 'under the skin' of the doctrine as it were, I can assure you it is quite unlike any other triune system.

We often forget that for most ... It is quite a mess.

This is just a rehash of the straw-man argument against religion.