People who play both are edge cases, if only because most don’t own both machines. Neither do I think PD takes much interest in Forza beyond its technical merits and keeping up with what the competition are doing.Not sure I agree with your track implementation. Are people really not going to buy Forza if GT7 has some new tracks? I don't think GT7 really cares about what Forza is doing as much as people think it does
But I do think Sony cares about winning headlines when Microsoft release a major title. Or being in the best position to sell software & hardware at Christmas.
In Aug/Sep the GT movie is generating the headlines. But Oct, Nov, Dec are the most important months for videogame sales. And you need to put your best foot forward.