I feel like the simple solution if you want to level up faster is get more members, and war more often. But..but...too bad.
I explained before why XP for 3 starring the whole map is basically a non-starter, and how titling the balance more toward winning than participation encourages large clans to keep most of their players out of war, or to form small elite clans that pretty much never take new members.
Bottom line, whatever the balance is, not everyone is going to be happy with it.
The idea of additional XP for a win streak, that's an interesting one, and something I actually proposed as a loot bonus before clan XP existed. Incidentally, I'd also like to see clan XP for reaching total trophy/point thresholds, and possibly total donations.
And yes, 3 starring TH9s isn't necessarily rocket science, but it's a lot harder than TH8s, as evidenced in part by the fact that my TH9 w nearly max defense, level 17 combined heroes and mostly level 7 walls hasn't been 3 starred by another TH9 in months. And not for lack of trying either.



