So - back when the clan quests system was released, a bunch of us expressed how much time it would take to reach the final tier of rewards. We were told this was short-sighted, and they'd be adding more methods to gain clan XP.

Looking at the list now, the number one clan in the world is at level 8. Our clan just hit level 7 today.  We started at level 4 at roughly beginning of August - so in two months we have gained 3 levels, while the top clan has gained four. The top-rank rewards require level 17. Even assuming the current pace of progression remains constant (~2 levels/month for top clans, 1-1.5 for average ones), that still means almost an entire year before we can get those rewards.

This seems excessive, especially considering the rewards themselves still require you to actually earn clan coins - a lego book is 3000 coins, which is about 3 weeks worth of quests.