Commentaries from dragon ball characteres many times tell us which character is stronger than other. But sometimes they seem to be wrong or contradict themselves later. With regards to Beerus, in the Dragon Ball Super manga in the times of the battle with Zamasu, it was said by Wiss if I recall correctly, than Gogeta might be as strong as Beerus. A lot of battles and training happened since that, several zenkais and Goku and Vegeta got stronger. Now in the Dragon Ball Super Broly movie, it was said by Goku that Broly might be even stronger than Beerus. If Broly is equally or stronger than Beerus, Gogeta has to be way stronger than him, since Gogeta showed to be much stronger than Broly. Is this so? Were Wiss and Goku just speculating or are there more clues sustaining the authors intended to assert this?
No it hasn't been proven Gogeta is stronger than Beerus. The only characters who have been proven to be stronger than Beerus are MUI Goku and Limit Breaker Jiren.
- Firstly, I believe the only character in the series who has the closes idea of how strong Beerus really is would be Whis. Hence, I would mainly be considering statements made by Whis with reference to Beerus's True Power.
- Whis had said several times that Goku + Vegeta working together would allow them to go toe to toe with Beerus. By Working together, Whis implies fusion. This could mean, Gogeta or Vegito could be potentially strong enough to defeat Beerus or be very relative to him in terms of power at the very least.
- Another important factor to consider is the time limit for fusion. Considering how powerful Beerus is, the fusion might perhaps not last long enough for Gogeta / Vegito to defeat Beerus.
- Whis makes another statement in the anime saying that Mastering Ultra Instinct would result in Goku/ Vegeta surpassing Beerus. Whis also says this to Vegeta when he fights Beerus in the manga and loses the fight. This more or less establishes the fact that MUI Goku would be stronger than Beerus.
Now with regard to statements made by a few other characters,
- During the battle with Zamasu, it wasn't Whis but Shin who says that Vegito might be stronger than Beerus. However, I believe the show has demonstrated enough reasons why we shouldn't take Shin's word seriously. For starters, Shin thought SSJG Goku was strong enough to defeat Beerus, he thought SSJB Vegeta was defeating Jiren, Vegeta would struggle against Pui Pui, had no clue of what Ultra Instinct was. The character has been displayed as someone who is very inexperienced and often jumps into conclusions and is in awe of what happens afterwards or is usually corrected or mocked by the Elder Kai about the same.
- The second comment was made by Goku comparing Broly to Beerus and yes, if that were the case, Beerus would be significantly weaker than a Gogeta or Vegito. While Goku has a much more better notion of how strong an opponent is in comparison to Shin, I believe even he might not know the true extent of Beerus's power. For example, Goku was confident he'd be able to defeat Beerus after attaining the SSJG transformation the first time around, that he was using only 80% of his power(Despite Beerus being significantly more powerful in comparison to that). Even in the case of Jiren, the more and more Jiren began to reveal his true power, Goku was in shock. For example, in Episode 123, when Jiren revealed a fraction of his true power, Goku was in such extreme shock that he dropped from his Super Saiyan Blue form to his base form. Even in case of Frieza, Goku had no idea Frieza was hiding a level of power that high until Frieza revealed his Golden Form to Goku
So in the end, it comes down to whether one thinks Gogeta Blue is as strong as MUI Goku and Limit Breaker Jiren. There is an obvious disagreement between a lot of the fanbase with regard to this and there aren't any statements made in the movie or in Dragon Ball Super to help establish this. However, based on Dragon Ball Heroes at least, MUI Goku was indicated to be more powerful and it being the highest level of power of the MC, it does seem to make sense to me. However, that is up to you to decide.
Its hard to say really. "Official" power levels have been absent since Trunks arrived on earth in DBZ. From that point on, speculation took over and its easy to see why. In all honesty, the numbers were already in the millions and with a long way to go it makes sense they would shy away from finite numbers. They did later release a power level guide but after Trunks' arrival on earth the numbers don't add up. I digress though. As far as Gogeta's comparison to Beerus, I fear it falls into the same category as everything after Namek. Speculation based on character quotes. A lot of things left to interpretation. They changed both fusions for DBS. Potara is no longer permanent but retains the remainder of its definition. Whereas metamoran (fusion dance) got reworked completely.
Beerus did say at the end of BOG that "between the 2 of them, he might have his rival yet". This points toward fusion.
Whis has also pointed out that working together they may be able to beat Beerus, but if they refuse they only way will be mastering ultra instinct.
That being said, there really hasn't been much mentioned in terms of Beerus' full strength. Beerus told Goku he was using 70% of his power, but I believe Whis, later when they were alone, said it'd been a while since he had to use nearly 50% of his power. I could be off, it might have been 40%. Itsbeen a while since I've seen the movie.
Outside of the Gods themselves, only Whis has any idea of what Beerus can do. That being said, Whis doesn't get genuinely surprised by Goku or Vegeta much. In fact, I think that only once each, and that was in the TOP. Vegeta's Limit Breaker and Goku's attempts at ultra instinct. Only one other time has he been surprised, that was in the movie when Gogeta was fighting. My answer to this is yes. I believe Gogeta is stronger than Beerus. Is he so much stronger that he can defeat him in 30 minutes? Doubtful. He certainly stands the best chance out of fusion options. Some would argue Vegito could, but Vegito would fail spectacularly. His time limit is far too low. He may be close to or on par with Gogeta in terms of strength but Potara's one glaring weakness is that the more power you use, the shorter the fusion. He lasted a whole 7 minutes against Zamasu. Granted Zamasu was immortal, but he wasn't a God of destruction either. Vegito owned him, but it took too much power to do so and he defused. Kefla lasted 5 minutes against the incomplete ultra instinct. Gogeta, at least for the time being based on the movie, gets 30 minutes regardless. That makes him the best option for defeating Beerus. Kudos to Toriyama and company for staying with the vague definitions on both fusions though. Keeps the debate going on who's stronger but with no finite formula, its all speculation.