The point isn't about receiving as much as a boost as G4 but receiving a boost, alone. Hybrid form has been consistently portrayed as the strongest by a good margin (Luffy kind of kept it up with Lucci when both in base, but needed G2 to match his hybrid), so we basically can't measure properly Oden's level in comparison to Kaido as long as the latter didn't use his best form.
On the other hand, I'd take his awakened form as granted. He's probably the ultimate Zoan user we will ever see in this manga and he's an emperor, so it makes no sense for Oda to not give him awakening. It is also unlikely that he has already used it because awakened Zoans look like a more bestialized hybrid form. We haven't seen Kaido's hybrid, so it is next to impossible for us to have seen his awakening.