It won't be Castle vs Necro on Jebus, but Castle vs NegroGosha on Jebus. And those are two very different things. Even if we consider Necro = NegroGosha, it still won't be a direct comparison of towns. Not infrequently, Gosha is played as a main hero for other towns (especially where there's no terrain penalty). Also, in the original version of the template, the necro dwellings and the necro center were nerfed. That would have been a plus for Necro, but not a significant one.
Comparing these towns on Jebus, I would immediately focus on level 7 units. How easy is it to pick up an external angel or dragon dwelling on day 1-2, and what dividends will that bring? Can both be built up without issues, and how does an angel compare to a bony, or an archangel to a spectral? What's the overall useful speed of units in MP? And let's compare the offensive power of both towns, for example, against a horde of Efreet Sultans, which often appear on GO... where it turns out that skeletons without Goshan are far from what you'd want. From my experience... you'd have to try really hard to lose as Castle with more or less equal spreads, and even with a slight advantage for the opponent. I considered Citadel to be a more or less real competitor, especially from the combination of easy and fast building of the mighty gray ones, and of course the notorious Crag Hack :)

According to HeroesWorld rules on Jebus, you can start with Gosha, so this option is being considered.

What bony are you talking about, what do you mean? You don't even always need to set up horses. Transformer, power-up, and go-go smash skeletons, while breaking Dragon Fly Hives, Griffin Conservatories, and whatever else you find. If you get a conveniently placed mini-Conservatory or a lotter Dragon Fly Hive, the tempo skyrockets. If you get 15 lords in a Pandora's Box, same thing.

A huge plus for Necro is that it doesn't particularly need gold for building; a couple of shallow mines cover its financial needs, and the rest are in chains, earning bonuses.

I ran 10 generations, skipping only obvious blocks. In 2 cases, I reached the center in week 1 (days 116 and 117 respectively). I never set up bony, set up horses about 6-7 times, never set up Citadel or Castle; if I had extra tempo, it's better to upgrade horses. Often I used witches as extra fat. A couple of times I upgraded zombies.

Castle, for all its army's strength, loses to Necro in tempo because it needs gold to gather angels, then archangels, and the breaking of Conservatories and Dragon Fly Hives starts later.

So yes, if Necro sits around dawdling, stays on respawn, and emerges simultaneously with Castle, then the archs [archangels] will decide the fight. That's actually why I say: the lower the skill of the opponents, the more often Castle tends to win on average—it's more resistant to dumb plays.

And Necro's strength lies in reaching the center a couple of days earlier than Castle and devouring key bonuses. After that, you can even go home or to a side respawn, accumulate skeletons; starting from week 3, time starts playing in its favor.