If he rarely initiates texts but replies right away, there is a good chance that he is not particularly interested in you.
The fact that he rarely initiates texts is indicative of a lack of strong or even true interest. In a situation like this, he is basically biding his time, preoccupied with other things.
You are rarely in his thoughts until of course, he receives your text. Now, he replies. This is one scenario.
Another scenario could be that he is allowing you to be in the driver’s seat. In essence, he is letting you do the lion’s share of the work. This is not a good sign. Guys typically like the hunt.