I do not believe the first law was intended to assert the existence of inertial frames of reference, else Newton would have said that explicitly. I think you may be extrapolating from Einstein.
More likely, the first law was intended to correct the then widespread Aristotelian conviction that all terrestrial motion eventually ceases.
However, as a standalone statement it is vacuous.
If you are saying that the First Law is unable to stand on its own, then I agree with you.
If you are saying that NewtonWorld is not just about the first world, then I have to provide a clarification. I, as the founder of NewtonWorld (just for this article) declare by fiat that it encompasses only the first law (plus Kant’s synthetic, a priori knowledge). I agree that the name NewtonWorld is misleading and I wish I had chosen a different name. So, sorry for the confusion.