The problem I have with people seeing all the content is that there's no mystery anymore.
Back when I played in Vanilla/BC, I never saw the end of the game, and I didn't care. I had plenty more to do and there was always the mystery of "what's in that raid?".
Then you realize that you'd really like to raid, so you do your research and you "git gud" as the kids call it, and then you form up a raiding group.
But, with LFR being so easy that a braindead toddler can do it, it pulls away the mystique of the raids for people who would otherwise have been incentivized to get better to see the content, as they now just press a button and AFK for 30 minutes every week. At the same time though, designing raids for < 1% of the players is really stupid, but then again, so is designing leveling content using 90%+ of the expansion's resources when you spend < 1% of your expansion time doing it and 99%+ doing end-game.
Source: This is coming from someone who played pretty much all of Vanilla-WoD, and has been both a "casual baddie" and a "hardcore mythic raider". I've experienced this game from pretty much every angle, and I have to say that it was always fun regardless, as long as you have some content to do. (actually, it got less fun as a hardcore raider; dunno if I'm just cynical now or what but the last 3 expansions sucked compared to the first 2+Vanilla)