DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

I was thinking about a necromancy enhancer.

What is the purpose of the ban? Is it to prevent upgrading vampires, or is it to prevent the hero from receiving a +10% necromancy bonus?

Then, my second question: Why aren't artifacts that give +5% (the undertaker's amulet), +10% (the vampire cloak), and +15% (the necromancer's boots) banned?
They are not difficult to find on HL maps!