I don't think using his second-strongest form is the same as holding back. The most you can say is, he's not going all out. And he sure is trying way harder than huffing and puffing Zoro against them.
In your wet dreams. For worthless weak fodder like Zoro, even G4 can seem like a ultimate move. No doubt G4 hydra would easily exterminate cockroaches like Zoro. But for gods like Luffy, G4 is nothing but g2 to him. Its just him wanting to clear fodder quickly (like how Luffy used G4 against Goki) so he can get on to the main fight.
On the other hand Loro already got exhausted from losing a simple clash against S-Hawk. ACOC for him is a ultimate move where he gets KO'ed even if 100% fresh after using it like against King even though enma is doing 90% of the work and his just being carried.
So nah, G4 for current luffyi s just base. And it still did nothing to him whilst Loro already couldn't cope after barely stalemating Kaku and then getting bodied by Kid hawk.