"I don't know how you've trained, but you've got an unbelievable power... You might even win against Freeza if you came here whole" or whatever definitely suggests it. Also, Piccolo feels he can help Gohan and Kuririn after Freeza just went to 530,000; while he'd get killed in a fight against him without fusing with Nail, he does think he can manage something while he outright dismisses managing shit against 4th form Freeza (initial) who isn't exactly 10x above him.
Like, the training gains make no sense, but the story makes much more sense if you assume Piccolo's over 200,000 somehow from training with Kaio.