Currently reading it at the moment. I feel like he speaks with more certainty on a lot of issues than the amount of primary sources we have would permit. Is the book well rated in academic circles?
It would be interesting to see more recent perspectives on this, but in the meantime you can have a look at this old thread where u/Tiako and u/Iguana_on_a_stick discuss some criticisms of Luttwak.
I posted briefly about this a little while ago here, including a link to a recent peer review of Luttwak's 2016 edition. Happy to go into more detail if you want!