Developing a Necromancer hero.

Looks like you haven't played much against Haven players. They'll give you such a beating that you won't even notice... especially if they have a lot of knights. They can take down two stacks with a single attack, so don't be so sure that you can cause a lot of trouble with just archers! There are also many other units in Haven that can put up a good fight. Haven's strength lies in the fact that knights move among the first!

Looks like you haven't played much against Necropolis. On a large map, in the late game, Necropolis has a much better chance, especially if it has at least one Haven castle. I already wrote about the knights; skeletons can easily take down fifty of them - what prevents you from turning Necropolis into a war machine? Finding a Necklace of Blood is also not a problem. So what if knights take down one stack and damage another at the beginning of the battle? They'll immediately be blinded by vampires, and the rest can be easily defeated. Archers are a problem, but a small one. So, gain some experience and don't make such rash statements.