Mihawk to EB Zoro: I can show you the difference in strength between you and I without the need of crossing blades at all.
It's the same for Shanks vs. Admirals. His presence alone is enough to make an admiral give up, due to the desperation.
Shanks is the closest being to Joyboy. Like being the unofficial Joyboy sacrificing his arm for the real one. That's why the strawhat went from Roger to Shanks to Luffy. with Imu himself standing before a strawhat as it symbolizes what he is afraid of. The man who casually walks into the holy land, dictating the Gorosei what to do.
Bro, what kind of sneak "attack" are you talking about? It was Shanks' anger from 5 miles away that paralyzed Greenbull. How can you even call this attack.