Di Resta ahead of Sutil? 
I disagree with this. Whilst it's true that Sutil scored circa 15 points more than Di Resta, I think this is a case of not recalling the earlier stages of the season. I'm not saying this because I am Scottish and have some connections with members of Paul's family, I'm saying it looking back over the course of the season as a whole. There was a horrendous patch for Di Resta in the middle third of the season where he was driving superbly but couldn't buy a point - being involved in incidents, poor reliability and a botched pit stop or two by the team that seriously hamered him - comparable situations did not happen to Sutil at any point. During that horrendously unlucky period, Sutil managed to score about 15 points (which accounts for the difference between them at the end of the season), and importantly it was this stage of the season that the Force India looked at its most competitive making those points slightly less impressive than those later in the season when the car was likely always only going to finish 8th - 14th depending on the race.
They were tit for tat in qualifying with Sutil taking the edge in that regard, but that's likely due to the fact that Sutil has been racing open wheel cars (of course in F1 for the past several consecutive years whereas Di Resta has had a few years away from them.
Force India were one of the main teams that consistently tried different strategies for each driver - hedging their bets that no matter the conditions, one would likely score points even if at the expense of the other. The majority of the time, the riskier of the strategies was with Paul's team / car. As such, he was often scoring points against the odds.
Overall, points do not tell the whole story here, and I think that all things considered, Di Resta's season wasn't just more impressive than Sutil's, but
far more impressive than Sutil's if everything is looked at in the correct and full context.
It seems that the team bosses see things the same way...
Favourite racing series: F1, Indycar, NASCAR, GP2, F3, Formula E, Trophee Andros, DTM, WTCC, BTCC, World Endurance... etc. etc.