Tbh it still looks within reason, especially since Imu was dominating and is comfortably taking Loki's blows. That being said, the much stronger hybrid is still up his sleeve.
It also begs the question how Shanks captured him, since with such high power difference, even his entire crew would be useless.
Inb4 it was just a friendly drink and Shanks packed him up while he was drunk, which wouldn't be out of character for Oda. Or it's like I said, just a plot device to have Loki unite with Luffy.