Team TBD was designed around a few characteristics: leadership, strategic thinking, technological savvy, and chemistry. Sure, it's fun to have 10 superpowered guys running around beating up women and children, but if you're going to hold on to your gains, sooner or later you're gonna need an army of underlings, and you're gonna need the tactical knowledge to use them to further your ruthless agenda.
Leadership/Strategy: Alexander the Great: the finest field general in human history, conquered more of the known world than anyone. Maybe the greatest military mind of all time, he had no equal in his time and no equal since. Alexander is always two steps ahead of his opposition.
Grand Admiral Thrawn: The greatest tactical mind in the Star Wars Universe, Thrawn has conquered hundreds of worlds - one more is short work for him, especially with the kind of army we'll be putting together for him. His understated leadership style and lack of ego makes him a perfect second-in-command to Alexander.
Batman: Though a bit of a loner, shows great leadership ability in a fight. Also known as the world's greatest detective, Batman has keen insight into the minds of those who oppose him. Batman will also be responsible for bomb disposal:

KG: Everyone will fight harder out of fear of what KG might do to them if they lose. This is especially true of KG himself.
Technological savvy:Brainiac: Expert in creating and controlling extremely advanced technology. His knowhow will be the cornerstone of Team TBD's technological strategy.
Tesla: The greatest electrical engineer and one of the finest theoretical minds in history - combined with Brainiac's technology, he'll be responsible for creating an army of robotic nightmares to topple the world's governments.
Voltron: Not necessarily technologically savvy itself, Voltron
is highly advanced technology. His inner workings will be reverse-engineered by Brainiac and Tesla to create Team TBD's robot army. If one Voltron can conquer space, surely an army of upgraded Voltrons can take over one measly planet. We'll also be miniaturizing Voltron's workings to create wearable robot suits for some of our more mortal team members.
Batman: The ultimate gadget guy, Batman is a talented inventor and mechanic. He makes the perfect lab assistant to Brainiac and Tesla. Or, he will, once he gets rid of that bomb...
Chemistry:There are no pesky do-gooders on this team - everyone involved will be on board with world conquest from Day 1. Heck, several of them have made it their life's ambition. Nor are there any flighty, unfocused, self-centered members like Zeus or Dr. Manhattan. Team TBD has one goal, and they will not rest until they get it, by any means necessary.
Sure, there are lots of alternatives out there, with immensely powerful members. But what are you gonna do when Voltron rolls up on you and KG, Batman, and Bruce Lee come storming out in mini-Voltron rocket suits? Team TBD will sweep over the world like a black wave, starting just as soon as Batman finishes up.

Man, some days you just can't get rid of a bomb...