Necropolis versus Orcs.

But aren't mass spells dispelled by Decay?

They are. But the hero only spends 0.5 initiative on them.

Blindness is dispelled by Warlords or the Warlord's Word, and you can also find the Dwarven Helmet.

You still have to find the Helmet and give up +2 Morale and +2 Luck. This is very unpleasant against Creatures of Armageddon. Especially in 3.1, where dragons deal -4 Morale/Luck damage.
Warlords under control cut down Goblins.
All that remains is the hero's attack against Blindness and Sleep (1 against 2), or the hero's attack against Sleep and negative Morale. And the hero will have more initiative than the Vampires. The situation is clearly not ideal. If the Warlords are under control and the Shamans are defeated, control over the Necropolis is guaranteed, no matter what.

I didn't calculate it with a calculator, but I don't remember such changes in the description for patch 3.1, and when you hover over it, it says 80%, although they like to give incorrect data, like with the warehouse for Orcs.

There were almost no important changes in the patch description. But everything was in the English manual for 3.1.

On that map where we were playing, there were a lot of forts, and almost all the money went to them.

Neither 5k nor 50k is a problem in the late game. However, everything really comes down to the ability to seize neutral castles. Most often, this is possible in the late game. Was it not possible in that particular game? Tough luck, donkey, i.e., not a problem :-)