The argument is because trunks is training in 450X gravity, he is 4.5 times stronger then Goku when he first transformed, and this power boost would be enough to beat Broly yes? Well sad thing is using anime to prove something isn't the best way to do so. Sometimes there are mistranslations and stuff. Like here for example.
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Trunks is actually training in only 100X normal gravity. Trunks struggling in 100x gravity would make him a little less powerful then when Goku beat up Ginyu. I bet you didn't know the anime overplays the like crazy huh. Fun fact, they never once mention about being able to blow up galaxies in the manga. They aren't nearly as strong as the anime makes them out to be.
Anyways, Broly >>> Kid Trunks
I say kid Trunks automatically wins for being a canon character however XD.