Gohan has recently emerged as perhaps the new strongest character in Dragon Ball Super, having fought toe-to-toe with not only his father, but also Vegeta and even Broly. Gohan’s Beast mode is a powerful new transformation, to be sure, but it’s one that he was only able to achieve in this timeline; in Future Trunks’ time, Gohan never reached this new level of power. So what made present Gohan so much stronger than his future counterpart?

https://screenrant.com/dragon-ball-dark-future-explains-reason-gohan-stronger-goku-vegeta/