Necropolis or Castle (Which one is stronger?)

In general, even nominally, the stats are roughly equal, and as for how it plays out in "live" games, everything is said in point 7.

There's no question of a tie, because if the 6th-level Humans are only slightly weaker than the Necropolis, then they are clearly superior in the 2nd, 3rd, 4th, and 7th levels.
The 1st and 5th ranks are almost identical.
For fixed and poor random maps (like Ring), Castle definitely has an advantage. By the way, Castle is also considered the strongest on Jebus (I haven't tried it myself).
And on CMs and similar maps, none of the castles has an advantage – it all depends on the layout.