It is a known fact at this point that Vegeta is perhaps the most powerful mortal fighter in the Dragon Ball universe, which is why it is always so scary when he becomes evil–something that happened both in Dragon Ball Z and Dragon Ball GT. However, where these two situations differ is purely in a matter of strength, and GT’s version of a corrupted Vegeta makes DBZ’s look like a joke.
Vegeta was first introduced in Dragon Ball Z as a villain who came to Earth with the intention of wiping out all indigenous life there in the name of Lord Frieza, and then selling the vacant world to the highest bidder. However, he quickly teamed-up with the Z-Fighters in an effort to defeat his former boss, which led to Vegeta joining the heroes of Earth permanently. Before long, Vegeta found himself married to a founding member of the Z-Fighters, Bulma, who had given birth to their son, Trunks. Vegeta started out as a universe-traveling, planet-destroying conqueror, but now he was essentially an earthbound retiree. That’s why, when Goku returned from the dead at the cusp of the Majin Buu Saga, Vegeta decided to let the evil sorcerer, Babidi, infect his mind and turn him into Majin Vegeta–thereby allowing himself to return to his original, evil ways and fight Goku without any of the mental or emotional hang-ups he’d have as a reformed hero. As Majin Vegeta, his inhibitions were down, and he didn’t hold back against Kakarot–which led to one of the most iconic fight scenes in DBZ history (though not the most impressive).
In Dragon Ball GT season 1, episode 27 (written by Daisuke Yajima, directed by Osamu Kasai, produced by Toei Animation), GT’s evil Machine Mutant, Baby, has come to Earth in search of Vegeta as he wished to possess the Saiyan Prince’s body and merge Vegeta’s power with his own to create the ultimate warrior. First, however, Baby had to possess a few other fighters while he searched for Vegeta: Goten and Gohan. In this episode, a possessed Gohan has challenged Vegeta to a fight, and Vegeta happily accepts. The two battle for some time before Goten arrives and shockingly assists Baby-Gohan. Previously, when Goten was possessed, Baby 'laid eggs’ in his mind which gave the Machine Mutant remote control over his actions, essentially adding Goten to the alien-robot’s collective hive-mind. So, with their combined strength, Gohan and Goten overpowered Vegeta, and Baby was successful in possessing him–thus creating the most powerful corrupted-Vegeta in history.
Baby-Vegeta is Stronger than Majin Vegeta, & it’s Not Even Close
When Vegeta went Majin and fought Goku, he proved to be equally matched with Kakarot, who was fighting at a Super Saiyan 2 level. Since Vegeta consciously allowed himself to be corrupted for the sole purpose of not holding back against Goku, fans know that he was giving it all he had during this fight. Skip over to Dragon Ball GT with Baby-Vegeta and fans will see that he is much stronger–thanks, again, to the comparative power exhibited by Goku. When Goku finally unlocks Super Saiyan 4, Baby-Vegeta is able to hold his own against him–which is way more impressive than Majin Vegeta, who could barely keep up with Super Saiyan 2.
Not only can it be confidently determined that Baby-Vegeta is simply stronger based on this simple one-to-one comparison, but GT’s version also has a power Majin Vegeta didn’t have. Baby, as a single entity, can add people to his collective hive-mind just as he did to Goten in this episode. This means that while Baby himself is within Vegeta, he can infect the entire universe with his influence–making him a cosmic threat the likes of which Majin Vegeta couldn't even fathom. For these reasons, it should be clear to any Dragon Ball fan that Dragon Ball GT’s evil Vegeta is way more powerful than Dragon Ball Z’s.