Hi Mister_Bruce, WOTR would be a sad game indeed if everyone had to take a Nazgul to be competitve. Not least since they are only a legal ally for Evil
Still Betrayer + Khamul + added wraith combos are a bit sad, I think I saw a pic about that online...I think a tournament with no allies makes a lot of sense, to be honest. Though they have it a bit $$$ backwards, since it is pinging the good lists a great deal to not even allow them their allies from the allies only list! It is a bit different when it is just allies from another list and players are cherrypicking the things that are better than their own casters etc. Stopping players from taking silly things like Corsair Arbalesters as allies makes a lot of sense. In this specific case, I would imagine it was player angst about Epic Tranquility (more on this in a second) that was at the root of it all.
But back to your specifc problem - Yes, take a unit or two of xbows, as suggested. Artillery is pretty iffy in this game but xbows are tough, mobile (with heroic shoot, overlorded if neccessary) and very hard hitting. Then take the greatest Evil caster of them all, Saruman. Use his Epic Ruination each round at range. Shatter shields, throw in the Exxiscates and bolts of fire, throw crossbow fire at the shieldless units just use your own melee troops to scree the real hard hitters in your list.
Now back to Epic Tranquility. It riles people, but they need to learn to throw in that heroic charge to beat it. If they do so, it will only work 50% of the time. This is exactly like the ability Saruman posseses, which works 50% of the time but no might is involved. I would go one better and arrange Saruman's unit with shooting LOS forward but a melee unit on either side and less than a base width between them, so it is impossible to charge and duel out Saruman at all with, say, Amdur.
Then take Lurtz and Thrydan, bounce them around your multiple units and hopefully there should be something that can charge and you get to move second to put the dueling hero there. Once you sort Khamul by trying to duel him twice, buring him up with spells will pretty much require him to fight you H2H.
Looks good in theory?