I think you need hard dollars and units as opposed to percentages here, since the gaming pie has grown astronomically since 2008, with genres and players that did not before exist. Namely music and rhythm games, the rise of the Wii, and dancing/fitness. The PS3 and 360 were also credited for growing the dedicated console audience larger than it was previously. We also have more PC games for casual players that were previously unavailable on console and made strides to cater to them once they arrived, like The Elder Scrolls and Call of Duty. So an inability to grow with the more mainstream influx of players does not necessarily reflect a retraction.

You're also mistaken when you say JRPGs conform with the modern game length since they only take 40 hours to beat, I assume you probably don't play those games so you wouldn't know. Most AAA action games can be beaten in 5-10 hours, the longest I recently remember is Deus Ex, at about 20. That is, unless they heavily recycle assets as I've mentioned before. Even then, Bethesda was only able to make about a 10 hour story in Skyrim.