I believe that the prices (and both the availability of capacity and the requirement to use it/pay for it) for Apple were locked in even before TSMC had the current 3nm process, as a certain source of revenue removing much of the business risk of building the fabs.

It is hard. But I hope they do. They need to paid their engineers better to compete. Their expansion to US are already costly. ( US engineers working in TSMC are already complaining about working conditions and salaries. I am not surprised. )

Apple doesn't always have to use 3nm, they could have stick with 4nm for another year and let other parties to pay the bill. But what if other parties are not interested at those cost. TSMC will be back to square one. So in reality it kinds of goes both ways.