Okay, so let’s distinguish between “difficult” and “time consuming”
If I gave you a very easy task - let’s say, every time your screen changed color, you had to click your mouse. Easiest task in the world, right? If I made you do that 5000 times in a row, is that hard now? No, it’s the same difficulty, it’s the same easy task, I’m just requiring you to do it a lot.
On the other hand, if I tell you to beat a boss in dark souls, it’s going to be pretty difficult, even if I ask you to only do it once and because you’re skilled at the game it only takes you 5 minutes.
Levelling in WoW consumes less time. You don’t have to kill 1000 rats, you kill 5. That’s not easier, that’s just less time consuming/less grindy.
It has always been weird to me that people mistake these concepts. I think it’s because they take a weird sort of pride in doing the same thing over and over again and they want to think that makes them skilled players rather than people who are just willing to do the same thing over and over again. I’m not saying this applies to you, but it’s a common attitude among “old school” MMO players.
Now - why is WoW less time consuming than it used to be? Several reasons.
When WoW first came out, there was only one continent worth of material, and everyone was new to the game. Most of the people who played the game were new to MMOs. There was no one playing the end-game and there was not a lot of end game content. Everyone was focused on the normal levelling/exploring process. So they wanted that process to last a long time. If people got to the end too fast, and there was little content, people would get bored and leave.
Now, 17 years later. There are very few new-to-MMOs players. Most of the new characters being created are alt-accounts by existing players, players who may have done The Barrens or Westfall 20 or 30 times by now. Additionally, there is a LOT more content. It’s not just that the top level is 120 vs 60 (it sounds like they may have reorganized this). That makes it sound like there’s twice as much content. But remember that levelling becomes logarhythmically more difficult. Going from, say, 90-100 under the old scale is probably like 10x the required XP as going from 40-50. There is probably 10x more content to level through, now, with a lot of expansions, than there was at the game launch. If they maintained the same rate of levelling up, it would take you 10x as long to go from a new character to the top level.
Additionally, there is a lot more content at the top level now, and a lot more focus on it. Lots of raids, lots of dungeons designed for top level players, lots of PVP - most of the content that people actually play from day to day is stuff you can only do at the top level. So that’s where most of the player population is. If they put a large barrier between a new character and getting to the top level, those people won’t have many people to play with, and they will take a long time - literally potentially years at the old WoW levelling up pace - before they can join everyone else to play the main content of the game.
You’re essentially applying the 2004 standards - where there’s very little end content, lots of new to MMO players, and only one continent worth of stuff to explore and do - to 2021 WoW, which has 10x+ the content, few new to MMO players, lots of top level players, and most of the game’s content focused on top level, and then, essentially concluding concluding “bah! casuals! they want it easy! new players should have to take 600+ hours to reach top level!”
Now - I’m not saying their solution is perfect. I haven’t played WoW in like 13 years. Maybe they could do a better solution, like, alt accounts level up really fast and new players level up slower. Maybe it’s too fast to get a good taste of the content. But using old WoW rates with the amount of content they have now, and the focus on end game, would be a daunting and mostly lonely task for new players.
Edit: What they really should do is operate a shard type system like Guild Wars 2, where there are no distinct servers (except for realm pvp), and instead it fills zones up with players, then opens a new instance of that zone, and fills that up with more players. That guarantees that you always have a good amount of players playing with you wherever you are in the game. It doesn’t become a ghost town because you live on a low population server or no one around your level is playing on your server at that time. It’s such an obviously better system now that I have a hard time imagining any MMO that doesn’t use it and who doesn’t just rush people so that they’re all the same top level working without it.