Leveling from 1 to 20 or 1 to 23 isn't just superfast when you play in a party. Did 1-17 in about 40min solo. It took me 2h to get to 24 (duo).
And this is just ridiculous. Gaining several Ranks for killing one enemy is too much.
I mean 1-20 should be way faster than 21-30, but please not 10 times as fast.

BUT
Without low rank content there is no real reason to change it. So we need way slower leveling and rank 10+ content.

But basically i dont understand why the sp system and requirements are so complicated in the first place. The RPG leveling system was perfectly fine 20 years ago, with a slight increase of exp required every new level.