It's a pretty good summary of the different factors, their cyclicality, etc. plus includes a few interesting graphs.
Johnson's main case seems to be for diversifying across factors:
Diversifying across complementary factors makes sense. Doing so will mitigate the aforementioned cyclicality associated with owning any one factor in isolation. While this could result in inferior long-term results relative to owning the best-performing factors in isolation, no one knows what those factors will be on an ex ante basis and few have the stomach to stick with them for decades. Perhaps the single most compelling reason to opt for a multifactor strategy is that it will minimize the biggest risk of all: that investors will bail on a factor, manager, or strategy when it experiences an inevitable period of underperformance.