In theory they are the same. In practice, they are not.
Build a product or service before you test is insane. It's like sending athletes onto the playing field without letting them practice beforehand. It's a recipe for failure.
Unlike requirements documents and wireframes, prototypes go further than show and tell and actually let you experience the design.
One of the most common pitfalls of following a process is being tied too tightly to it. If you're more focused on the process than the end goal, you won't be successful.
I prefer putting a time limit on "sketching time". This forces the sketchers to work quickly without getting caught up in the details.
If you can't explain your concept in less than two minutes, then something is probably wrong with it.
Start with quantity, exploring lots of ideas. Quality will come later.