My 16-month theanine self-experiment

From the discussions I've seen about theanine, the real benefit supposedly came when it was taken alongside caffeine. The thinking being that theanine moderated some of the jittery effects of caffeine, allowing the user to take higher doses of caffeine, which itself has some benefit on task concentration and focus.

I wish the author had spent time addressing that theory specifically.

Correct, this is why tea and especially ground tea leaves like matcha induce the feeling of focus for longer, they already naturally have higher levels of L-theanine with caffeine.