Xizor will have the home-field advantage where-ever he goes.
No one wants to be ruled by a rampaging Sith. Traya is too subtle to ask for help from locals, and Kun is ruthless and has tons of scary-looking followers. He'd probably rather eat the people of the galaxy, instead of get help from them.
Xizor, on the other hand, is charming, has pheromones, isn't pure evil, and has the power of a galaxy-wide organization with lots of wealth. I also bet he's a great propaganda machine (or Guri is). If there was ever to be a ground battle with Xizor and Kun/Traya, Xizor would have the help of the local population.
Remember the rules:
[LIST][*]The arena: the known galaxy.[*]No outside help of any kind, the combatants cannot call upon assets outside their power base, or other prominent powers apart from those listed below e.g. Mandalore the Indomitable, Darth Nihilus.[*]No outside involvement, other powers will not and cannot interrupt or affect the battle, for the purpose of argument they are non-existent. [*]No surrender, fight to the death![*]No alliances, combatants cannot ally themselves for any period of time with other powers (excluding non-mutual tactical ceasefires etc.)[*]Combatants can wait their opponents out, but not if only one remains.[*]Technology level is universal (unless considered archaic or advanced at the time): blaster fire, armouring, lightsabers etc. are all the same regardless of period, all that matters is size, quantity and power.
No outside help of any kind so Xizor's pheromones and charm are useless here, nobody can bring in the locals for help. Xizor's just got Black Sun resources. Kun's got his support, Traya has her support.