Take an MMO and do this.
You level your character from 1-20, at level 20 you have to do a long arcing quest to choose a sub-class (L2). After that is completed, you have to do an instanced quest where if you die once, you have to restart it. Make the difficulty semi-decent but not too hard.
Once, they pass, they can finally choose their sub-class. They level another 20 levels and now they are level 40. Rinse and repeat, but this time, make it a bit harder, but they still do an instanced quest and if they die once, they need to restart.
Keep doing this at lvl 60, then 70, then 75, then every 2 levels until lvl 90, then every level till 99, then every 0.33 level.
Thus, when someone is level 100, it actually means they earned it instead of it being a function of time.
Instanced quests can only be done solo, are class specific, or if not solo, may include NPC bots. There can be other goals other than surviving, like finishing in the right time.
In reference to items, the difference between gear has level off and not be exponential where everything is based on gear. Where skill matters.
Then again, making a cash shop with higher tiers of weapons where you'd need like +35 to do a level 100 would be a sinister way to model it. You'd get people paying the cash shop just to progress their character.
But the goal is to make a higher level actually mean something. Or you could do a tier system with gold/silver/bronze and tiered awards and whatever.
Just a thought I had.
p.s. I'm already pre-empting someone saying, "already done that in XYZ games"
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