You're acting as if he was completely useless. They give him other abilities in the manga so that he's still able to help out instead of just giving a transformation that puts him on par with Goku.THE MANGA FUTURE TRUNKS ARC!!
Were Trunks can't do jackshit but Goku learns God of Destruction exclusive techniques off screen.
Yeah no.
The Dragonball Super anime is pretty awful at this. You have a character who is as strong as Goku just by fighting poachers. A character who was relegated to a house wife be stronger than Goku. Krillin who quit training and become a cop and got injured pretty easily whole he was doing job strong enough to make Goku go blue. You have Roshi be just as strong because he was secretly training lol. And the other Saiyan from the other universe. It's ok if you like this, I'm not a fan and prefer the manga over the anime. Super as a whole is pretty weak tho, I just can't help watching it because it's DB lol