The damage was done before Xbox One. I called it that Xbox was in trouble several years prior to the launch of Xbox One, and no one believed me because they were still riding high on 360.
I got a 360 at launch over a PS3, and didn't get a PS3 until far later. But quietly over that gen, Sony started PS+ and had free online, free games, and their first party was slowly starting to be impressive. During the 2nd half of the 360 gen, MS had multiple casual-friendly E3s with almost nothing to show except Nike workout aps, Kinect, or timed Call of Duty marketing or DLC deals. Their first party was hollowed out during the 360 gen. It wasn't until PS4 that Sony finally hit their peak in terms of first party and the contrast was laid bare.
Xbox One was always going to be worse off, but people were in denial about it for at least the last 3 years of the 360's life because they were invested in the ecosystem and didn't want to admit it.
I jumped back to Xbox this gen after I saw them making a lot of correct calls, and adding value for gamers again (like Sony initially pioneered on PS3 with PS+ / free online and then later abandoned). I just jump back and forth depending on which company's head is inflated with ego like a balloon, and which one is trying this gen.