This is false information that people always pass off as fact to fuel their argument. First off this low percentage number is for the people that cleared everything or was on the hardest raid, not the amount that participate in raiding. People started this crusade against raiding when wow devs said only a low percentage of people stepped foot in naxx 40. Now people use this to claim low percentage of people raid lol.
It funny you list those games and say only a low percentage raid. Yet some of their main end game content to this day is raids. With features now like automatic group finding, more people than ever are participating in raiding content. If only 3-5% of people do raids it seems kind of silly for those game to continue making raids don't you think? They continue to make them because a large portion participate in some degree.
On the topic, KoTFE might have been financially successful but it fails as an MMO. Obviously there is no way to tell for sure unless the 1st quarter 2016 report reveals it. However if you have working eyes and are aware of your surroundings. At KoTFE launch population never got as high as previous expansions. Then the months after there has been a big drop in population across all servers.
The only reason some servers like Harbinger, shadowlands etc are doing well is because everyone is abandoning the worst pop servers like pot5, jung ma, and bastion to move there. In the end even if this KoTFE direction they went is just as good financially or slightly better it is still a failure. Your job as an MMO is to keep people playing the game for as long as possible. Not play for a few days and move on to something else so there is less people in game to play with.