the one thing you're forgetting is oda is a fore-shadower. If he mentioned who and how many luffy wants in his crew, that's how many there'll be.
Like the lastest foreshadow. BB said he's going to put on a show that will shake the world. And what happens? he gets wb's power and literally shakes the world. Luffy said about 10, there's going to be 0-2 members. only question is who if any.