"a function of the size of your character pool, because if your password is short enough for n-1 to contain a significant percentage of possible combinations then it's probably already short enough to brute force anyway"
This seems to say that a small character pool, aka "n-1 containing a significant percentage of possible combinations", implies that your password is "probably already short enough to brute force".
So small character pool means that "probably" the password is short/weak.
I'm saying that a small character pool does not imply that a password is "probably" short/weak.
And to be very clear: Using the size of the character pool to say it's "probably" weak is a form of "reliably predict[ing] if n is sufficient".
What am I misreading?