And what exactly does that have to do with being "afraid"? Shanks came to Marineford with way less force to face a much higher force than Kidd represents, challenging Navy, Schichibukai and Blackbeard pirates, with all parties agreeing to not messing with Shanks. Why are people capping so much when it comes to Shanks? Kid invaded his territory, Shanks told him to choose whether he leaves his Road Poneglyph behind and retreats or faces
him. Note that,
1) Shanks said that
he will fight Kidd if he doesn't retreat (setting up a 1 on 1 himself)
2) As
@Garp the Fist stated, it is in character for Shanks to offer his foes a moment to reconsider fighting or facing the consequences, he did it multiple times.
As for Teach, he went on trial and error as he didn't know whose path he will cross, while his other commanders are on a mission of their own. Do you think that, if Law sailed right into Blackbeard's territory, he would've told his best forces to stay back?
Also love how you try to make it look like Shanks
needed the help of the giants when we know Shanks actually did them a favor. Shanks is their sworn brother, they love and respect him. Being of help is of greatest honor to them. Given Shanks' power level is vastly superior to those two giants, how would they be of help to him?
What's next? Whitebeard asking pre skip Luffy and Buggy to lend him a hand in Marineford means Whitebeard can't do it on his own and is in need of their help?