What's the system they don't fit?
From what I've seen so far, we are going with a lone striker, who needs to be fast and press hard to force errors, which then allows our wingers to score - like the Vardy of old. I've also seen that we need a striker that can hold the ball up and bring in the wingers - like Iheanacho.
It's not immediately clear what the expectations of the striker are, nor why Vardy (or maybe Daka if he ran a bit harder) wouldn't fit.