The safe withdrawal rate answers the inverse of the accumulation question: no longer "how much do I need" but "how much can I take out without running dry". It is expressed as a percentage of the portfolio's starting value, not of each year's value.
It depends on four things: the horizon (thirty years supports more than fifty), the asset allocation (too much fixed income lowers the rate as surely as too much volatility does), the costs (every point of fees comes straight out of here), and the flexibility (being able to cut spending 10% in a bad year changes the arithmetic entirely).
A "safe" rate is not a guarantee but a probability. Any figure you see comes with an implied success rate attached, and it is worth asking what that is before building a life on top of it.