This is just lawlessness; there could be all sorts of options here, and the Cloak of the Undead King has nothing to do with it.

What possible option could there be against even 5 stacks of ГО in each?

Even a regular necromancer without a Cloak of the Undead King on HL can out-necromance own.

Out-necromancing is one thing, but out-powering is only possible with terrible diplomat luck.

the diplomat will join all sorts of trash.

With that trash, paths are cleared by scouts, the same scrolls are picked up, Griffin Conservatory/hives are taken...

various scrolls and 4 Dimension Door and .. relics behind shifted guards

You might get lucky, but in my experience, it's a rarity. 4 Dimension Door are good for clearing the map; without real troops, this is impossible, unless 10 angels were gathered by 124 — but that's already a case of overwhelming skill. And only if on the 2nd week the well-fed diplomat can't take (all) utopias with scouts himself.

And if there are no suitable options, then it's quite possible to do without them.

I didn't quite understand.. I meant that with a small starting army, fighting with clerics and raising various wisdom or eagle eyes is tough.
Let's agree that on an HL+U map with lucky roads, the probability of getting diplomacy up to 13 is about 80%, and then the chances are equalized.