Your definition of a 'system seller' is subjective, vague and pointless. When a consoles sells well because it has an A B C D E F G shitload of great games, there's no point in complaining 'yes, but it doesn't have 'just' A and B'.
Having 7 games worth buying a console for is better than just having 1 or 2 games. In no way does this mean game A and B are worth more than C D E F G. It simply means game A or B are worth more for the platform to sell well.
In a sense, a console having 1 or 2 system sellers is not a good sign.
When you look at the history of gaming platform and games being glamoured as 'system sellers' it's because:
a. the platform was selling poorly and relied on just one or two franchises to keep it's sales up: Halo (xbox), RE4 (GC), Monster Hunter (PSP), MGS4 (PS3), Titanfall (XBone), Mario xxx (Wii U)
b. the platform was an anomaly called the Wii where people bought 30 million copies of Wii fit/sport/play each
You're using double standards here.
You can't state Nintendo's first party games are systemsellers for the Wii U and at the same time state that better selling games like FIFA, CoD, GTA aren't systemsellers for the PS4.