Why does our bottleneck keep moving?
Because solving a bottleneck almost always means the next step takes over. That is not a failure but the nature of a chain. What does help is measuring where the waiting time sits rather than where the complaints come from: those two rarely point at the same step.
Can you forecast what we will need?
If there is enough history, yes. And that is the honest condition: without a few years of usable data a forecast is an expensive guess. We first check whether that history exists and say so when it does not.
What if we know something is wrong but not what?
Start with the New Data Scan. One day on site, fixed price, and afterwards you know which step in the chain should be measured first and what that delivers.