I think you may be missing the point here. All one length so that the swing is the same for every iron. It's not easier to hit a club if it's a different length than all the others. Some one length systems are based on the 7 iron length and some the 8 iron length. Both of these irons are typically the ones people are most confident with. You swing fully with every iron except your highest lofted iron, for me it's my lob wedge which I use 70 yards in. Woods are typically based on, I believe the 5 wood length.
If the system was based on your easiest club to hit, the PW, you would not be in the ideal straight up position. At least this is my understanding.
Lastly, I believe the driver, wedge, and putter are called the scoring clubs.