Gohan was the weakest Saiyan even at base level while PIccolo during the Android invasion is at least as strong as Namer arc SSJ Goku since warrior-type Namekian have stupid high innate potential for gains.So how strong is Gohan at this point? Goku considered his lack of Super Saiyan as the biggest reason for being held back, so he shouldn't be too far behind. He still likely gets one shotted by a serious Piccolo though.