Tactics against Necromancers.

it's not a matter of taste here, the minotaur is the strongest warrior in the Dungeon based on maximum damage; he doubles the dragons, while their minimums are roughly equal. And considering that specialization gives + 1 speed and by level 12-14 minotaurs have higher attack and defense than manticores, there's actually no one else to choose from

this development scheme is for Impossible difficulty on an XL map; what's wrong with it?

Ah, so that's how it is!! With such a development system, minotaurs won't enter the fight anytime soon... Maybe in TE, and I'd agree with Das on Ferz, but in SoD, and even on King... only Shakti works here!!
On the first day, you need to find money for a second hero and for upgrading troglodytes! We get around 150 Hell Troglodytes with speed 7 (on their own terrain + specialization), who can take any dwarf settlement, any crypt, and even a small conservatory on the FIRST day!!! That means immediate money, resources, and even angels; and if you have Angels at the start of the first week, you don't even need to build up other troops! If you're lucky, you can find an external dwelling of dragons/manticores/minotaurs, which is also opened in the first week, and a summoning portal is built!!
With this layout, by the start of the second week we have: 1-2 angels, 200 Hell Troglodytes, 4 dragons/8 cats/12 minotaurs - we go to the enemy and kill them!!! Not even a prefecture is needed!!

the necro has 1 less, and by taking diplomacy in that 1 slot, for example, you can get a solid +

Aaaaaah, well if you're playing with diplomacy... then building up the Castle isn't necessary at all! In practically all rules, joining troops is forbidden, although some play without any rules at all and are happy; it's a matter of taste...
With diplomacy, it's a completely different game... Now Rampart with Ryland, Castle with Adele, Tower with Kira get the advantage.... IMHO - it's just not the same anymore...