While you're developing a game, there's going to be a lot of things that won't be coded yet. Many of them are simply going to need to be stubbed in until you can implement them fully, or somehow worked around.
Which ones get what treatment is going to be very particular to your game, and your development style. There's no wrong way to do it. Do what works for your situation.
Yeah imo it’s definitely worth prototyping the core gameplay without the proc gen — not only does it let you test faster it also lets you experiment with features and designs that you may want to include in your generator without having to code them first.
If you're 100% confident that your planned gameplay is fun, and if the procedural generation is the only thing involved that you're not yet 100% sure how to do, personally that's the only time I'd build it in from the start.
You need to get to the point of testing actual gameplay as fast as you can, and how the tileset was generated probably(?) doesn't have a huge bearing on that at first so it's worth doing the fast way.