He was considered the most effective fighter next to Goku and Vegeta, it was only his schedule that prevented him from entering the tournament. At the very least, he would be as powerful as Piccolo was during the tournament -if not, more powerful.
There is also something weird about Gohans power in Dragonball Super. During the Beerus Saga, Gohan is still regarded as being in his prime and the most effective fighter against Beerus. However, as soon as Freeza appears he loses his Mystic form and Super Saiyan 2, and he can barely turn into a Super Saiyan.
It's sad.