Necropolis or Castle (Which one is stronger?)

If there is no magic, with identical stats (and hero level) and with the same development pace (it's not just about skill here... but also about the map, so that you can build Angels by the second week/Archangels by the third week), then the Undead will definitely lose to humans and not only to humans, they simply won't be able to keep up with the speed.
Because in Heroes, nothing matters as much as SPEED, then DEFENSE... and only then everything else...

So, when everything is the same, the task again boils down to the stats of the monsters themselves! I already said that the human army has stronger stats than the Necromancer army, but there is one caveat.
You suggested a development scheme for the Human Castle until the end of the third week. Build Angels in the second week, Archangels in the third week. This is very difficult, but possible. But where will you get the money for the army, because after the listed constructions in the castle, it will hardly be possible to build an army, and you won't even be able to buy all the Archangels. And the Necromancer can come at the end of the third week with the entire army (except for dragons) and even if you sit in the castle, there will be nothing to defend with.