I believe those are two ways of describing the same thing. If you're able to book some fab capacity, that means you get to decide what the fab does with the next wafers in the queue.

From your sibling comment, I think you're interpreting the 3x HBM stat as contributing to making wafers scarce. It's more that the next wafer to be processed in a fab is especially precious, making the opportunity cost larger. The beach sand remains plentiful.