I can accept Jiren because he isnt some random saiyan from U7 who has been there the whole entire time undetected. Now we don't know where Broly came from as its not explained yet but I'm assuming he is from U7. Jiren on the other hand was from a completely different universe so he never came out of no where because Beerus told us there were other universes out there during BOG.
But if we assume Broly is from U7 then whats the explanation for him not being found or known not even by Whis? I know an anime doesnt have to follow real world logic but an anime should follow its own basic logic. Broly being alive this entire time in U7 and not being detected by Goku or Vegeta for this long doesnt make sense. But who knows how the movie will explain it, maybe the explanation in the movie will make sense we will have to see.
And I just cant see a saiyan who has been MIA this entire time being stronger than Goku and Vegeta man. They train with Gods and Angels on a daily basis, how is a saiyan who went most of his life not even being detected by these guys going to find the time to surpass them? What exactly has he been doing to get this strong? Theres nobody out in the universe thats stronger than Whis besides zeno the other angels and possibly his attendants and Goku and Vegeta spar with him often. Whether Broly is some legendary saiyan shouldnt matter at this point, because he wouldnt be stronger than their teacher. It just feels like a big slap in the face to all their hard work for Broly to just show up out of no where and being head and shoulders above them. How would you feel if Goku just got SSG and was head and shoulders above all the GoDs? I doubt you would like that.
"How would you feel if Goku just got SSG and was head and shoulders above all the GoDs?"
Ok I dont know about you but for me I will accept it and just went with this new reality.
Super Saiyan God is a new thing and full of mystery just like Jiren. Furthermore SSG is no longer a normal Super Saiyan transformation, its actually a transformation that brings out God Ki. We cant speculating this or that towards SSG the first time we saw it.
Ok let say the first time Goku brings out his SSG power and we found that this power went beyond Beerus' power, I dont think its a big problem. The story just merely telling us some new information and that's GoD Beerus's power level is actually lower than SSG power level. We are not new to something like this right? long ago Jiren was being hinted many times to be stronger than Belmond and we never complained about it at all. And if we take GoD power Toppo and put him against Jiren, Jiren still would overwhelm him.
So we back to the main point of discussion, LSSJ is a unique transformation from U7, its not SS Berserker transformation because that only applies to Kale fron U6. So LSSJ transformation is as unique as Jiren's power and it is as unique as Kale's SS Berserker form.
The key thing that you should take note;
"Don't assume any unique transformation will be similar to normal transformation"
In Naruto verse we have Hashirama. A very unique individual.
One keyword for you
"Unique"