This isn't a straight-up fight. Both teams are given the objective of eliminating every opposing member of the opposite team. The Illuminati has its base in New York in Stark's tower. While the Cabal has its base in Latveria in Doom's castle. Which team would succeed? Assume both teams work well together.
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Illuminati: Iron Man, Reed Richards, Professor X, Dr. Strange, and Black Bolt
vs
Cabal: Norman Osborn, Dr. Doom, Emma Frost, Loki, and The Hood
Considering the Illuminati at the time were before WWH!
Strange in the day feeds the Cabal their worst nightmares. Dr Doom unfazed.
While Reed blasts Loki with Celestrial kill gun.
Ironman kills Osborn.
While Prof X handles melts Namors brain and holds Emma.
Emma reverts to diamond form while Blackbolt messes her up. Doom holds with shields depleted and tries magic but Strange matches while Tony locks hands.
Team then kills Doom.
Loki returns pissed and the combined might of the team scares him off.
Cabal is mor pro-active and less constrained, they would hold the world under control before the illuminatti if they all had the same goal and worked well toghether.