It seems to me the main problem with the tournament is the imbalance of the towns. And nerfing Necropolis itself will have little effect on that. Necropolis will become weaker, Conflux, Dungeon, Rampart, Castle will become even stronger. Then you'd need to weaken those towns as well, for example, by banning the construction of birds in Conflux, the upgrade of elves in Rampart, the upgrade of Troglodytes, the Stable in Castle, or something along those lines.
And even then, you won't achieve balance with such methods, especially since the balance will change from template to template.
It seems to me it's simpler to just make a table of fixed bans when two towns are played on a specific template. Take the opinions of the top 3 best players on a given template as the data source and average them out. Obviously, everyone has their own preferences for what the ban should be, but at least this would roughly even out the balance.
