It can be argued that WB's Bisento is one-half of his main fighting style, which is the Gura combined with tons of raw physical power, which backs up his Bisento. He utilized it many times in tandem with his DF powers, and at times attacked powerful people in lieu of it. WB's Bisento is far from a throwaway combat style.
WB has used his Bisento in serious fights all the time. He chose to use it instead of the Gura to intercept Kizaru. He used it against Akainu and had their first major clash with it. He used it in tandem with his DF for the entirety of the war, used it to incapacitate Teach, which a Gura blast failed to do, and chose to clash with another Yonko using it, and struck at Aokiji with it. You think Whitebeard would do so when using his Bisento is just some toy to him?
Gai was called the best Taijutsu user. There's a difference between best Taijutsu user and strongest Taijutsu. The former directly indicates that someone is the most skilled at doing something, while the latter is someone is the overall strongest of everyone in this category.
When did I say this?
Because Shanks is a coy jokester and wasn't being literal?