The conclusion sounds about right for linear SP AAA games. SP games can still sell as demonstrated by a number of titles, some recently, but none of them are linear or short.
Uncharted 4 can take 15-25 hours to beat and that's perhaps the most successful AAA $60+ linear title outside maybe Mario Odyssey that came out recently.
Fallout 4, Witcher 3, DA Inquisition, GTA 5,both Tomb Raiders, Far Cry, Watch Dogs 1/2, etc... none of these are linear or short SP games.
For other examples, P5 or Nier are considered successful with 2 mil of sales, but these are lengthy games and not AAA.
It's just not worth the risk to AAA publishers to sponsors a linear, shorter experience that will cost $60 mil - $100 mil when they can do something more profitable with both money and staff.
Edit: Forgot to mention that I think Let's Play Videos on YouTube that just basically post the whole game are also probably detrimental to sales (those that present interesting snippets and commentary on the other hand could be helpful).
That's not going to affect say longer RPGs or fighting games but I can't help but think that it's not good for those 6-10 hour linear story oriented games