It is true the sire progression is quite slow around 20 and up. Then again it is supposed to be a MMORTS so there needs to some limitations on progression.
The way it is now, you still progress, but it is really random on how fast if you are free or can be quite fast if you pay additional money; you can keep shuffling until you get nothing but purple quests.
Cannot say I like the latter, I know it is FTP and there is a shop but I can't shake the feeling those who dump tons of money are just going to dwarf the free players.