He appears to be better at providing useful feedback on how to improve a car than Kvyat.
Although Kvyat clearly out-drove Hartley in Austin in terms of finishing position, the Kiwi actually recorded a faster lap time and exceeded more expectations than the Russian based on their comparative recent experience.
Qualifying speed was always going to be the toughest thing for Hartley to master.
Driving the car right on the edge, as he needed to do on a qualifying hot lap, is something that only improves with time spent in the car and the more a driver gets to know its idiosyncrasies. It was his first crack at driving a single-seater since 2012 let alone the cutting edge technology involved in Formula One.
In the short term, Kvyat looks the more likely to score points for a team which is in a mid-table battle with Williams and Renault in the constructors' championship.
You could probably understand the logic of alternating the developing Pierre Gasly and Hartley alongside Kvyat in the remaining rounds this season.
But the fact Toro Rosso have opted to go with Gasly, who has only two F1 races to his name, and Hartley (one) for this weekend's Mexico Grand Prix would indicate the bigger picture is more important to them.
If Hartley can continue to build on what he did in Austin a fulltime drive in 2018 seems more than likely.