You missed part of my point entirely. First off I said that TBC was a partial example, not a full example. It's also disingenuous on a few grounds because these are entirely different eras. It's not just about raids it's also about dungeons, and dungeons have been invalidated in more ways than one after initial launch of an expansion until Legion came out.
Dungeons weren't invalidated in TBC just like they weren't in WoTLK, and the only reason they weren't was because people were forced do them. The difficulty was flat in dungeons and the rewards were terrible outside of the first couple weeks. The game just forced you to do them for the badges you could get at the end. The challenge and difficulty of these dungeons are gone almost immediately, but we are forced to do them because of busy work.
LFR existing doesn't really change my point about raids being invalidated either. People have, and almost always have done the path of least resistance in this game. The amount of people that joined my guild back in TBC who didn't beat SSC/TK were numerous. Why? Nobody cared to go back and "see" the fights, and the only reason people went back to "see" fights is because gear was attached to it. I assure you most people clearing content dropped both SSC/TK the moment they were able to spend time in Hyjal/BT, just like people dropped Hyjal the moment Sunwell came out. Unless there was a reward attached (trinkets in BT, Warglaive's, or DST), people dropped old content fucking immediately. Maybe you're in the minority of people who just want to see shit, but most people took the path of least resistance, did the content they were able to do and that was it. Most people farmed badges in both TBC/WoTLK to get powerful gear, and they did this by taking the path of least resistance (Heroic dungeons and Karazhan).
Before you cite attunments, they removed most of the relevant ones or difficult ones after they realized how ridiculous it was to force you to do Kael'Thas in TK half a dozen times for a single raid group (not accounting for new recruits, or bench players) because of the limited amount of water the boss dropped.
Again, LFR didn't cause people to stop caring about raids. Most people didn't care about clearing the dungeon a single time, regardless of whether or not there was one difficulty. People did what was easiest for them and acquired gear that was easy for them to get too. People dropped raids that weren't useful or had very little rewards, and this happened in every expansion for every type of player. The assumption you make about why people farmed badges to begin with are also pretty silly. Most people farmed badges because it's all they could do. These people weren't interested in doing raids that weren't easy, nor were they interested in 'skipping' content. Just like you mentioned, badge gear alone wasn't going to allow you to skip content, but that's assuming people wanted to do content to begin with. I know so many people whose only interest in TBC was doing Karazhan each week and getting badges. Why? Because it was the only way they could get gear reliably and that content, along with heroics was easy. This also speaks volumes about game design, because you start to see the need for more 5-10 man content, as these people weren't interested in pursuing raiding at all (25 man at the time, fixed difficulty, and just two 10 man raids). This led to multiple difficulties in WoTLK, every raid having a 10 man variant, and ultimately setting up Cataclysm/MoP to have an alternative to 25 man raiding at the highest difficulty, with them splitting the game into 10/25 man.
Not going to get into sub numbers because it's a very convenient fall back for people that really don't have a leg to stand on. If you want to argue about what made WoTLK great, I'm all ears. But if you're only retort is it was good because it had subs, well, why even have a discussion? My argument has and always will be that WoTLK was pretty bare bones and was propped up by a few things that later expansions didn't have. One, people wanted to see what happened to Artha's, and two the game was 4 years old at the time as opposed to 14. I'm not excusing bad game design by Blizzard over the years, or less popular expansion features... but to expect the game to grow constantly for 14 years is pretty unrealistic. Could they have curbed sub loss over the years better? Yeah, probably, but people are living in a fucking fantasy land if they think any design choice or feature additions would have continued to make the game grow.