Imho, the scene of Shanks-GB was way overhyped. Imu reacted in the same way at Joy Boy haki, but Imu Isn't a lot weaket than Joy Boy for sure (and Shansk's haki was even hyped by the giants) and now one even tried to say It. However, with GB someone did try.
Also, opposite of Imu, GB Is over the top with his reactions, we saw this against Momo too (
https://worstgen.alwaysdata.net/for...mples-of-greenbull-acting-like-a-clown.59070/), and anyway explicilty retreated in front of Shanks'
whole crew.
He said It himself and even said that It wasn't the time to fight them, not even that he won't fight them period:
Kaido himself had King with him (and didn't have to deal with the mugi, Kidd and Law too) and still retreated in front of the RHP. And Shanks didn't even have a wrinkle on his short at MF, Kaido didn't even fazed him lol.
He Is just Oda's golden boy, even compared to Joy Boy as we saw. That + film Red promotion + Ryo being histrionic + him taking about the RHP as whole + the already impossibile situation + Kaido's past example are enough to explain what happened.