Comment by tcai

As peterjmag indicated in his comment, 9^9^9 looks like 9^(9^9) which is actually greater than 9!!. A different way of looking at it is n! < n^n. We can see from here that factorization isn't really the new paradigm that the author is looking for; it's just a part of the exponentiation paradigm.

Furthermore, factorials don't really scale or stack easily. What the author is getting at in the relevant location is stacking the same concept: 1. Multiplying is just adding the same number several times. 2. Exponentiation is just multiplying the same number several times. 3. Tetration is just exponentiation several times. 4. Etc.

This allows us to generate the infinite hierarchy easily expressible by the ackerman numbers (which is basically A(i) = f_i(i,i)), which doesn't generate itself as easily with factorialization in place of exponentiation.