Well in all fairness to Kvyat, he did step in later in the team by getting demoted from the mothership. that has it's effects on 1) morale, 2) motivation 3) ability due to different car and environment.
Also, kvyat had a lot of bad luck technically too,
all of which are not taken into account in the stats provided (obviously the stats are for the races between Kvyat and Sainz, but the 'other influences' are not taken into account.)
For example, Carlos had zero of those 'stresses' put on him , so it's not really a fair comparison as it never was a fair situation to begin with. One might wonder how Sainz would have reacted to what has been done to Daniil.
I think rather than 'Daniil' having something to prove, i think it's more that Sainz has something to prove.
Even if Daniil has his head back level and let the past be the past, no matter how you put it, he still carries that 'treatment' in the back of his mind, AND one might wonder if he's going to stay in RB house after 2017, whereas Sainz has still a year more to go without too much danger of losing his seat.
Also, as Sainz himself likes to claim so much that he's just as good as Verstappen, and had [lol] just as good a race as Max in brazil [lol], and Verstappen is rated so darn high, and Kvyat not so high [good and fast, but not 'the next boy wonder'], then lets be honest here, Sainz should 'have a walk in the park' against Kvyat.
The reality is though, that if Kvyat actually is level with Sainz, or actually beats him regularly, it's probably end of career for Sainz. After all, what use has RB on two drivers that are the 'exact' same but can't put anywhere anyway becuase the mothership is occupied by their very best. It's still a 'junior program' team so one of them will get ditched for example for Pierre Gasly. Also, if Kvyat beats him fairly consistent, then Sainz' popularity in the field goes down hard, too.
If a team would be eligible to choose between either driver (including RB that is) then Kvyat first of all is the most experienced, also has had his down and came back on his feet, and then he's more marketable due to his Russian roots [Russian sponsors and money].
So really, the pressure is on Carlos, not on Daniil.
And lets be fair, people aren't looking set to 'expect' that much from Daniil anymore next year, so the pressure is off next year for Daniil. If he still makes clumsy mistakes then yeah, he'll probably get replaced by Gasly mid-season.