Have a look at the PS3 - expensive, hard to code for, didn't even have rumble for the gamepads, terrible controller with really bad triggers and a very unstable network (PSN at the time) and didn't even have any progress tracking like Xbox live (achievements etc), it was actually reported to be the biggest let down after the success of the PS2 in gaming history. Sony did turn it around, but it was worse then X1. I know, I owned a launch PS3 and even as a diehard PlayStation fan the PS3 was a nightmare.
The X1 comparable to the PS4 wasn't and still isn't as good for most - it has its moments and strengths but it most certainly isn't the biggest disappointment in console history. Its just hasn't done as good against its nearest rivals, and came off the back of the xbox 360 which did extremely well in sales.
Yes Sony turned it around and managed to eventually match 360 sales. However, XB1 is so far behind PS4 I can't see them catching up in any meaningful way. Happy to be proved wrong.