I like to think of it as an exponential curve with a decreasing slope, leveling out as it goes higher.
See, your graphics can always get better but more detail requires more money, manpower, and computing power so there are diminishing returns as you get closer and closer to photorealism.
What companies should focus on is aesthetic. I can think of plenty of games that were far from photorealistic but still marvelous to look at (Zelda OOT, Super Paper Mario, Minecraft, FF6 to name but a few)
See, your graphics can always get better but more detail requires more money, manpower, and computing power so there are diminishing returns as you get closer and closer to photorealism.
What companies should focus on is aesthetic. I can think of plenty of games that were far from photorealistic but still marvelous to look at (Zelda OOT, Super Paper Mario, Minecraft, FF6 to name but a few)