Pre-cadence ranking question - Hooktheory I, sec. 4.2

I am going through the Hooktheory I book. The review question at the end of Section 4.2 says “Rank the basic chords I, ii, iii, IV, vi in order by their utility as a pre-cadence chord.”

I don’t see where this is explicitly explained in the book. I understand that IV and ii are common pre-cadence chords, and iii has the least utility because it is more restrictive. Can you better explain the ranking: IV, ii, I, vi, iii?

Using the definition of a pre cadence just being a chord that is going to V. IV and ii are explicitly discussed in this context as being one of their primary functions so they are the the most useful, and as you say iii was shown to not work well before V. Regarding the ordering between I and vi, one could really argue for either (I would probably group them together). ‘I’ has a stronger relationship with V so that’s why it was put first.