As half-saiyans, Gohan and Future Trunks theoretically have a ton of untapped potential that could lead to them becoming stronger than their fathers, but even with their differing circumstances, neither Saiyan has ever been able to make the most of this. Dragon Ball Z: Kakarot follows in Dragon Ball Super's footsteps, granting Goku and Vegeta God Ki and incredible new transformations such as Super Saiyan Blue, but in terms of both story and gameplay these new transformations leave Gohan and Future Trunks in the dust, making them obsolete characters all around. Thankfully, Dragon Ball Super also holds the key to making them relevant again, though it would require some changes to be made in game.
As it stands, Gohan's best transformation caps out at a 150% boost to his stats, while Future Trunks' best transformation only provides him a measly 50% boost to stats. Both of these pale in comparison to Super Saiyan God which provides a 200% boost to stats, but given that both Goku and Vegeta are going to be getting another power increase in this next DLC, that disparity is only going to increase. Since both Gohan and Future Trunks are fan favorite characters, it would be good for Dragon Ball Z: Kakarot to bring these characters closer to the power level of Vegeta and Goku.
Gohan Transformations in Dragon Ball Z: Kakarot
Ironically, before any of the DLCs came out, Gohan was one of the strongest characters in the game due to his Ultimate Gohan transformation being so powerful. The 150% boost added by this transformation was on par with Goku's Super Saiyan 3 transformation and was much stronger than Vegeta's Super Saiyan 2 form, and Gohan's stats were nothing to laugh at either. Super Saiyan Blue will probably provide a 250% boost, though, meaning Gohan is falling behind quickly, but Dragon Ball Super doesn't give him any new transformations.
Despite not getting any new transformations, Gohan reaches a power level on par with Super Saiyan God and potentially even Super Saiyan Blue through training. The best way to represent this would be to add more nodes to his Ultimate Form skill tree, perhaps allowing it to be leveled up all the way to level 6. In that case, Gohan would be able to reach the power level of a Super Saiyan God, but still wouldn't be outshining the newest Super Saiyan Blue transformation. This likely wouldn't happen until DLC 3 though, as Gohan was infamously pretty weak during Golden Frieza's return.
Future Trunks Transformations in Dragon Ball Z: Kakarot
When Future Trunks first makes his debut, he is the most powerful Z Warrior on Earth. Goku had yet to return and Vegeta still hadn't reached Super Saiyan, so Trunks' feat of destroying Mecha Frieza was truly amazing. Now, though, he has yet to unlock Super Saiyan 2, 3, or any other form, meaning he is one of the weakest playable characters in the game. In the anime, Trunks does obtain Super Saiyan 2, but in Dragon Ball Super, he goes to a level beyond that which not much is known about.
During the final confrontation with Fused Zamasu, Trunks enters a state which has become known as Super Saiyan Rage. This looks very similar to his Super Saiyan 2 form but he has a blue outline around him, suggesting that he somehow tapped into a source of Godly Ki. This form is incredibly powerful but equally short lived, and in the anime Trunks can't tap into it at will. If this form is implemented in Dragon Ball Z: Kakarot, it will be interesting to see whether it provides a 200% or 250% boost to his stats. He would be skipping a 150% form just like his father, though.
Dragon Ball Z: Kakarot is available now on PC, PS4, and Xbox One.