The bad perception of Admirals is Oda fault too, Greenbull scared of Shanks coc because of Film Red exit in August
He got sneaked by an usage of CoC never displayed before, that wasn't a mere CoC wave like some try to make it be (from the strongest CoC user right now)
And Greenbull's personality is kinda similar to Queen, he is a little bit overreactive, we can see it by how he talks and poses, kinda similar to Kizaru too, but Kizaru's body language is different
All the Admirals have quirky personality traits
Also GB said he couldn't fight the RHP at that moment, Shanks was previously talking with the Gorosei.. do the math