If it were, Karin would've at least noted so, rather than having the only measuring stick for Goku's power being that he was slightly above Karin. Nothing suggests Goku's power had made much of an increase until he drank the Choshinsui.
If it were then wouldn't Goku have gone after Piccolo-Daimao straight-away? He didn't know he became young again. You could argue he didn't know he got stronger, but even then Karin never says that Goku became leagues upon leagues stronger.
I don't believe in the whole "retroactive Zenkai" bit, but even if I did it'd have to be one hell of a Zenkai to overcome Piccolo's 200 vs 210 advantage.
Goku would get thrashed. He acknowledged that fighting Piccolo again instead of drinking the Chōshinsui would lead to his death, and he didn't know about Piccolo's youth power-up at the time.