So, when he says it has a lot going for it that other games can't even claim to have, it just boils down Museum pieces, and Manufacturer movies
Of the three games, Pcars2 is the only one without a livery editor. Forza has one that is top notch right now, as it sits. GT has the possibility to one up everyone, but that depends entirely on the importing feature. If they can show us that with absolutely minimal restriction, than it will be the best. Either way, this is an aspect that the competition has, so it's not really part of the list.
Each game has a photomode, scapes are a part of that. How each game mode goes about it is different, but the competition can still very much claim a prominent photomode within their games. GTS has a ton of scapes, but they're restricted. Pcars has a ton of tracks that they can use for photomode opportunities, but doesn't have staged settings like GTS does. Forza probably has the least opportunity here, but Forza vista at every track is something that the competition doesn't have. They all have their plus's on this side of the fence, but again, it's something prominent in all of the top 3.
Manufacturers Cup/Nation Cups can very well work like spec races. That they have a certain restrictions within their guidelines for a certain race isn't any plus over any other game. Each game will have their own restricted events with a ruling system.
Campaign mode. There is no reason to go into detail about this. The top 3 have it so far, and to a much more prominent degree than GTS.
Like I said, it's fine that you want to do those things, I do too, but it didn't answer the question about what makes it the 'official driving game' nor did it really show that its doing things that the competition can't even claim to be doing.