Yes, I agree that these are highly dependent on your circumstances.

My figures (so far as they were properly thought out at all) were based on my estimate of the most likely ways for me to reach the relevant level of wealth. I can think of four (none of them either very probable or spectacularly improbable) and none of them would make me benefit a lot from a PA, but for sure there are people who would benefit far more and might have good reason to employ a highly skilled PA.