Though, in seriousness, what is this mystery thing Jonathan has? I can think of a bunch of things just off the top of my head.
On one hand, he has both the training and expertise of the Belmont AND Morris families.
He also has Charlotte's repertoire of knowledge and magic.
He has the insights and wisdoms of Wind, who being a ghost would of course know things ordinary humans wouldn't.
He has a far greater arsenal and knowledge of weaponry than the average Belmont or Morris; in fact, Jonathan's experience in combat variety rivals that of Alucard or Soma, even. This applies to conventional weapons as well as subweapons, as he goes far beyond the traditional knife-axe-cross-holy water routine.
He knows how to utilize the Dual Crush which, when studied and modified by more magically-inclined allies like the Belnades family, could likely be crafted for use by a single person while still retaining the immense power of the technique (Julius' Grand Cross, anyone?).
He knows how to execute his mission with a partner. While this isn't a huge thing on its own, one must remember that for a thousand years the Belmonts have done their jobs solo, with very few exceptions. That ability to cooperate with another with a different set of skills without hindering either of you is definitely something I feel noting, especially given that the DCW were won by more than just Julius' skills alone.
He has a motherfuckin' teddy bear that's serious fuckin' business.
So, given the half-dozen ways I just took it myself, any chance you could be persuaded to divulge that little bit of information, plot?