Sorry, OP, not reading the whole thread, so this might cover stuff already covered.
First, when Ion says each level should feel meaningful, he's not talking about how much time goes into attaining that level, or how much time you spend at a given level. He's referring specifically and only to the rewards you get for attaining the level. Right now on live you can go 10+ levels without attaining anything meaningful. You don't get any new spells or abilities, and you might get a talent but in some cases they're pretty moot as well. It sucks pretty hard. So by introducing the level squish as well as introducing more abilities back, you can get a new spell or ability, a new talent, or some other key feature (like pvp or dungeons or the mastery stat) every level, or at least very close to it.
Second, I do think that they should adjust their approach to the process by not speeding up the leveling process baseline. Instead, they should keep the speed of attaining level 120 (soon to be 50) as-is, but further augment the heirloom system to allow people to adjust their leveling speed. Give people who want fast leveling the tools to go fast. Give people that like the leveling process time to enjoy it. Everyone always talks about this like it's some kind of binary, when there's already a mechanism in-game for this very specific thing.
As to your comment of people forgetting, "What this game is about," sadly, it isn't about that anymore. The game has completely changed. It's an end-game focused game now. Classic is there if you want it, but as we've seen with Classic too, everyone focuses on the fastest leveling possible to get to end-game there. The players themselves have changed. People just want a game that's different from the one you want now.
As for why people don't enjoy leveling, I can't speak for everyone. But, for me at least, leveling is... incredibly boring. Even in vanilla, leveling was really boring. Doing quests and killing mobs is a snore fest. Padding it out longer just makes it that much more tedious for me. And people say, "Well, they need to go back to the way Vanilla was, when leveling was hard." Leveling has never, and will never, be hard. It's tedious. It takes zero skill and a ton of time. Some people consider a high time investment a type of difficulty. The people who hate leveling are not those people. I don't feel rewarded for spending 8 hours gaining a single level. I feel relieved the level is finally over. Leveling can't be a high skill ceiling activity, because it's something every player needs to go through. It sucks, but there it is.
As to leveling being a key part of RPGs, I have to disagree. I play a lot of RPGs, and I generally tend to ignore levels as a whole. The only exception to this is TTRPGs like Dungeons and Dragons. Leveling is far from my most focused part of the game. But leveling in D&D does truly feel meaningful. But that's due in part to the fact that you only have 20 levels, and the entire game is focused around the story that you're living right now. That isn't how WoW is. I'd argue that's never been how WoW is. Leveling was always a goal to attain. I don't know anyone that plays D&D to gain levels. As soon as you turn leveling in D&D into a goal is when people start just mindlessly doing random encounters to maximize XP gains, and suddenly it's now WoW and sucks. The only time I've ever cared about leveling in RPG video games has been... CRPGs, which literally are just Dungeons and Dragons in video game form. But I'm also still so preoccupied with everything else I'm doing in the game that getting a level is a nice fun moment. The fun parts of WoW are locked behind max level. The only thing to focus on while leveling is leveling itself. And I can only enjoy leveling when I'm focused on the things that are fun, and I happen to level.
If you could somehow make the leveling process in WoW the Mage Tower, I'd love leveling. But it wouldn't be because gaining levels is fun. It's because the Mage Tower is fun. Massacring boars for the 10 millionth fetch quest is boring. AFK AoEing in a normal leveling dungeon is boring. Nothing about the leveling process is, or has ever been, engaging. I need skill based (not time based/tedium) leveling to feel engaged. If leveling was like that, low skilled players couldn't level.