As much work probably went into GTA V and RDR2 as went into the games from 2008-2012. They're massive, I dread to think how many man-hours are going to be put into GTA VI, they always have to one-up themselves.
Games just take a lot longer to make now, especially openworld games, but look at other developers.
Insomniac (PS3/360) - 10 Games: 3 Resistance Games, 6 Ratchet & Clank Games, Fuse.
If crossgen games count towards the oldest they release on like you do then the following developers look a little worse:
Bioware (PS3/360) - 6 Games: 3 Mass Effect Games, 3 Dragon Age Games
Bungie (PS3/360) - 4 Games: 3 Halo Games, Destiny
If we look at the Halo series irrespective of the developer you can see the releases have slowed down. The 360 got 4 new Halo FPS games, the XBO currently has 1.
Bethesda developed Oblivion, Skyrim and Fallout 3 for PS3/360 and on PS4 only Fallout 4 and 76. Skyrim released 5 years after Oblivion yet here we are 8 years after Skyrim and who knows when TES VI will come out.
Mostly the only developers releasing as many games as they used to are the almost annualised games. Far Cry, Assassins Creed, Fifa, Battlefield, Call of Duty or AA games rather than AAA.
Insomniac has released more than 3 games although they are smaller in scale than the games mentioned. They seem very experimental this gen. Spiderman was very out of there comfort zone as well.
I count games that released at the same time as part of the newer gen, Look at manhunt 2. So bioware gets dragon age inquisition. They also had a game cancelled among other complicated stuff behind the scenes.
As I mentioned in the original post I understand that games take longer to make. I understand that devs can't make as many game as in the past but the drop off for rockstar compared to others is ridiculous. Going from 10 games to 1 is not good. What happens next gen? Do we just get nothing from rockstar?