All we know for sure about RoF-era 1st form Freeza is that he casually beat the christ out of Tagoma on the daily... And Tagoma was stated to be equal to Mystic Gohan. That makes 1st form Freeza =/> Bootenks at the very least.
Then you have all of the Z Fighters acting like 1st form Freeza already possessed the strongest ki they had ever sensed at the time.
So yeah, not sure.
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They all had sensed Super Buu, too. And Buuhan was only like 2.5 times stronger than base Super Buu, in the first place.
Meanwhile, first form Frieza was confirmed to be above Super Buu, going by statements, and Frieza on Namek went from 530k all the way to 120 million, from first form to final form- which is over a 226x boost.
Applying that to his first form should make him well over 100x stronger than Buuhan, AT LEAST. Even if that Vegetto could have gone SSJ3, he probably wouldn't have been that strong. In SSJ1, he was probably only about twice as strong as Buuhan- not ****ing 100x stronger than him, lol.
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