Again completely different situations.No, characters can say what they think, it won't become the truth especially if they have no proper knowledge about what they are talking about.
You must be registered for see images
Naruto can that gaara's sand is the best defense but it would obvious;y be false because he hasn't seen jutsus like susanoo or mokuton.
This isnt about hyping a character's abilities. Tsunade obviously can restore his arms because she was going to but knowing Orochimaru she couldnt trust he would not attack Konoha. Which is the ONLY reason she did not restore his arms.