Creating a MMO leveling experience where players have to slog through boring or needlessly repetitive content in order to unlock the "fun" part is bad design.
If your game has a gameplay loop where you're laboring for a reward, that's going to create resentment quickly. Jeff Kaplan regretted adding golden gun skins as a reward to the competitive mode of overwatch.
I’ll say something even more controversial. I wish we would’ve never added any cosmetic items to Competitive. I think the people playing Competitive should only be there because they really care about playing in Competitive mode, and they want to rise through the tiers – that’s who I think belongs in Competitive. I don’t think we should overly incentivize players because of cosmetic rewards into the system any more than we already have to the point where if we could do the Men In Black thing and make everybody forget and we would come out with Overwatch again and literally wouldn’t add any cosmetic rewards to the system, so it’s tricky because we get asked the question a lot. Now, that doesn’t mean that all the cool stuff that we have ideas for couldn’t be given out to players in other ways, so it’s not like we’re just not going to make it, like “Haha we’re taking out football and game over” – it’s more that I would love to give it out in a way where it doesn’t encourage players to be in Competitive mode who don’t want to be there. I think it really takes a really special mindset to be in Competitive, and I think a lot of the problems that we see are players who really don’t want to, or belong there, spending more time than they should there.
-- Jeff Kaplan
Prior to the gun skins, players in the competitive mode were playing for the sake of competition, and people who didn't want that environment were in quick-play. After they added the gun skins, the competitive mode attracts players who are willing to have less fun in competitive for the reward of the gun skin. They're laboring for a reward.
The MMO analogue is something like doing your weekly trivial PvE lockouts in instanced PvE games. After your 4th month doing the same raid without wiping, do you actually want to be there? If the bosses didn't drop loot, how many times would you go? Are you laboring through the PvE content for the gear-reward, or do you actually have fun in the raid?
Why does the game make us labor for X hours through the "unfun" part in order to earn the reward and "be allowed" to play the fun part? Why not let me play the fun part right away? Why not make the whole game different sorts of fun parts?
The traditional answer to these questions is they slow-feed these abilities and game systems in order to not overwhelm the player. The first 100 hours is an extremely long tutorial designed to gently onboard players. We can do better!
I think the main thing that games can do is make the player ability on-ramp faster: give better players access to their whole toolkit sooner. Don't prevent those players from fighting against more difficult mobs (make the fights more about player ability and less about character stats), and reward those players with better xp/h. A janky and unintended example of this is solo mage zf leveling in classic wow.
The secondary thing is to get rid of the hard separation between the leveling grind and gear grind. There's this weird trend in MMOs where you don't participate in any of the power systems except leveling up as you level up. You can make crafted gear, buy stuff on the auction house, enchant your gear, grind BiS for you level, etc. But why would you ever interact with those systems when the main questing process gives you a constant stream of good-enough gear and all of the content is trivially easy? It becomes a waste of time to visit the same dungeon multiple times for the BiS pants when you can spend that time just questing and leveling up, which replaces your pants with quest-pants soon enough.
To fix this, we want to make sure that the most efficient way to play the game is to perform the end-game gear-grind fun-part, but at lower levels. Embed gear-grinds in the leveling loop. A brutish solution is something like what Albion has where monsters have "ranks", and so you take big penalties against T5 monsters unless you have the T5 reaver trait.
For a leveling MMO, instead of going straight from 1 to max in a continuous way, maybe we can sprinkle in hard gear-checks to progress into new zones or fight the new "tier" of monsters. That way before you can start doing level 11 content, you need to collect out-of-the-way gear from the level 1-10 content in the same way that once you hit level 60, you need to collect your pre-BiS before you start doing raids and whatnot.