Thanks for writing in. This is common misconception. So let me explain.
You are correct that the plan delays the weighed pack carries until the final 8 weeks. This is intentional and here is why:
Most folks who come to us for training help are aerobically deficient. We strive first to correct as much of this deficiency as possible in the first 16 weeks. Adding heavy weight hikes will impact that aerobic work negatively because those are muscular endurance training. The theory for this well explained in our books and in several articles on this site.
We see this misuse of muscular endurance training often and it one of the leading causes of this aerobic deficiency. With our a string aerobic base you will not maximize your muscular endurance work.
We have used the approach for over 20 years on hundreds if not thousands of athletes form some of the worlds best alpinists to rank amateurs with great success so we stand by it 100%. If you read some of the success stories on the site you’ll hear from many folks who have followed this plan with great success on Denali and Aconcagua and Everest.
I well understand that this may differ from what you have heard from other sources so you are wise to ask for clarification.