but we're talking about GT trunks. these trunks are different trunks seeing as the adult trunks you speak of was capable of sustaining super saiyan while GT trunks found it difficult as if he was new to it. they are clearly different trunks
But by that, you MUST be implying that in the 5 years since dragonball z, trunks has gotten significantly weaker. I know that everything feels less powerful in gt (some could argue that the cell arc fights had less scale than the namek fights), however according to the story, the people of gt are not weaker than their z counterparts. Sure, trunks didn't train much likely, but at least according to the z version of adult trunks, its implied that he trained at least semi regularly (same with goten). They were lazy about it, sure, but they trained. So if we accept that z adult trunks is >> future trunks, making the leap that gt trunks <<< z adult trunks seems kinda far fetched
