As somebody who wrote all of the above (and a lot more) I call B.S. on this one. The amount of unique stuff in each subfield is not that great, and if you have

As somebody who wrote all of the above (and a lot more) I call B.S. on this one. The amount of unique stuff in each subfield is not that great, and if you have a wide and solid base in different subfields, picking up the unique ideas and techniques isn't that hard or time consuming. But after a generalist has it, he is a lot more productive and creative because he often applies stuff from other subfields to come up with better/novel solution to the problem at hand - something a specialist cannot do.