I have been leveling a lot on the Alpha testing out the new systems and believe I can answer any questions you have.
It does seem like you might have missed something though.
There is the standard leveling path that hasn't changed.
1-x is Classic, then x-y is TBC and Wrath etc.
Whatever they were in BFA they were just squished in number by 2 where applicable.
However, what you might want to see is the new Chromie Time leveling.
This allows you to pick any expansion and level through just that if you prefer.
For example, level 10 in the Jade Forest or Zuldazar.
I have two series where I did just that that might pique your interest and answer some of your basic desires.
If you have more detailed questions, post them there and I will be happy to answer them all!
Here is what I have so far
No Spec DK leveling through Classic / Cata (which is considered its own pathway atm, not seperate ones)
https://www.youtube.com/playlist?lis..._JZY21udzC7Uyp
And
2h Enhancement Shaman through MoP. Found out doing so that you can do all max level content MoP has in each zone, including dailies, timeless isle etc too
Still uploading them as we speak
https://www.youtube.com/playlist?lis...0mzGV-seJkrD7-
Check em out and if you have any questions lemme know!