Disclaimer: I don't own One Piece.
An immense number of people thought Monkey D. Luffy an immense idiot. They thought him a child that didn't understand any thing. They couldn't understand how he won any battles. Sheer lucky, they'd mutter. They couldn't comprehend how such skilled individuals would follow him, take orders from him, and be loyal to him. Did want to understand how he had 'brainwashed' people so apposed to pirates to turn tail and become one.
What they didn't understand was something they couldn't.
Monkey D. Luffy heard and saw many things. Just because he saw and heard things didn't mean he had to let on about it. The more you surprise people the better advantage you had.
He crew, his loyal crew understood. They might not have at first, but they did now and that's all that mattered. They saw that Luffy was right. He was useless at many things, but that didn't mean he didn't have skill. Just as he had declared when he was fighting Arlong, he could blend talents together to make the best crew.
People didn't understand, couldn't understand, wouldn't understand. They only saw a fool leading about wasted talent.
But that's alright. The people that mattered knew, and besides, Luffy would show the world. He would be King of the Pirates.
Yes, yes, my first attempt at something of this sort. Pitiful I know.