For EXP rates, you're supposed to gain experience through doing activities such as questing. The weights for different activities is relative to the main questline, which should keep your main class on level for the quests you're doing!
As more content is added, such as bounty hunting and the endless dungeons, leveling alternate classes will become much easier.
I didn't boost the EXP rates for stuff like popping enemies for the first release since there isn't much in the way of combat in side quests outside of the main storyline, so it felt unnecessary.
It's not as bad as it was at the time I posted that comment. I wasn't kidding about the game giving about a fiftieth of a level per each very long fight, but that's not a relevant complaint anymore since the last time I played (about a week ago), it felt better in both fight length and XP gain.
Next time I get around to playing, I'll have to poke around and see what's balanced and what isn't.
I didn’t touch the exp gains or anything in the last few updates haha. It probably helped that I added the option to start with a class instead of having to find them in the world.
As for combat balance the next update will be both massive stat overhauls, and complete combat reworks for the classes so balance feedback on the current build won’t be super useful!