He's so wrong about the nav cluster being redundant...
NumPad is much faster and more comfortable than the number row once you have a non-zero amount of practice with it, but you need to be able to control where the numbers are going without having to switch modes in between entering a number and navigating. Assuming that you are using your right, presumably dominant, hand on the NumPad, you can press the arrow keys with your right thumb, and the six-pack by stretching your right pointer, or you could control the entire nav cluster with your left hand. Either solution allows simultaneous rapid number entry and navigation with little or no wrist movement.
Ideally, you'd also have a pointing device integrated into the nav cluster area as well, which would allow you to move the cursor long distances without having to move hand positions to resume the low stress precision control offered by the arrow keys, or having to take your dominant hand off of the NumPad. Note that the first advantage will also be realized when navigating through a text document as well as a spreadsheet, and that the hand spread required will be less than that of a TKL while maintaining all of the functionality of a full size. Many companies, including IBM, Focus, and Access-IS, have experimented with versions of this configuration, but unfortunately, it remains uncommon.