At first I was confused on how SE could make a system like this work when you play multiple classes/jobs on 1 character. I've been through this before in Eden eternal, and leveling other classes was quite a horrendous system compared to your first one. Then I noticed the different varieties to level up that have been mentioned and noticed that it could actually work.

Main Story- The main story already gives good experience right now. This quest line will probably help your first class/job, maybe even your second if you don't just focus on one. This will probably make your first class/job easier to level since the first one is usually the hardest.

Class Quests- I don't know if they're still staying, but if they are then they can really help make leveling different classes a more unique experience. Hopefully they increase the amount that there will be.

Jobs Quests- These give a good amount of exp currently. They may add more but it could just possibly stay the same.

Leves- They said that you can pick them up at other places than the adventurer's guild in 2.0. This will probably be the repeatable quests that are going to be given out per camp.

Instances/Instance Quests- This will probably where the main source of party exp will take place in. With the content finder it will be easier to join these instances to get a continuous flow of exp.

With this I could definitely see it working.