Without Apple, there would be other mobile devices, surely? It was an idea that was in the air. Arguments about Apple doing it better or quicker or differently don't have much bearing on your specific point here.
There were, windows phone and android, but neither could prove the Spotify model that offering a free tier led to paying subscribers (and at least Android had enough market share for this to be certain), something their entire existence was built on and something the labels questioned a lot. People seem to forget this part entirely.
Now you could argue everyone on iOS would pay as happily on Android if there were no iOS, but then you argue fiction against reality.
No, my argument is what actually did happen, in this reality. There’s no need for any experiment to be run to state what events led to what is today, and what would happen in a another reality like the one you described in your first post is irrelevant for the subject at hand.
Apple provided Spotify the platform they needed to prove their business model, it really is as simple as that.
True without context, but not if you worked there at the time. It’s hard to describe just how much iOS did for Spotify at a crucial time of the company’s existence.
But sure, we will never know for sure, but certain outcomes have far higher likelihoods than others.
Now you could argue everyone on iOS would pay as happily on Android if there were no iOS, but then you argue fiction against reality.