There are three elements in Wallerstein’s wrestling: Strength, Reach, and Agility. While all are important, it is implied in the introduction that each technique will emphasize one element more than another.
The element of Strength is not just brute power, it also takes into consideration stance and balance. Someone who is too upright or otherwise imbalanced cannot use their raw strength and will be overcome by someone with better leverage.
Reach is the ability to place the hands and feet in the correct places. Again, it means more than just the length of ones limbs. While they don’t outright say it, they are implying that flexibility is also important.
The final element is Agility. This covers the ability to use pulls, punches, and arm breaks quickly and decisively as well as making it hard for the opponent to do the same. I almost think the word “skill” or “alertness” is just as appropriate as agility for what they are describing.