The concept of spending 20+ hours of leveling up before you can get to the fun stuff of raiding needs to go away entirely. The journey was apart of the core of the Vanilla experience. The leveling journey has not been a part of the core of WoW's experience for well over a decade, and only serves as a barrier to entry, both for new players who want to check the game and for current players who want to play a different class.
Remove levels entirely. Allow anyone to create a character, be inducted into a short fifteen minute tutorial that walks them through playing their class, how to perform their role within a raid, and explain basic raid symbology (being able to distinguish damaging AoEs you should step out of from healing AoEs you should step in, etc). After that, the player is ready to queue for raids.