Straight to the point:
Supercell should just drop the star rank and put points instead. These points could be equivalent to star count multiplied by an inverse proportion to the weight of the base. Since it's an entirely different concept than clan wars, how we earn points should be different as well.

It's been a while since people are complaining about the "matchmaking" of the league. Supercell guaranteed that with time this issue should be solved, but it's been 3 months and we are still facing the same problems.

Let's say it happens an attack where a TH9 gets 1 star on a TH12. The value of this one star shoud be much greater than 3 stars resulting from an attack of a TH12 on top of a TH9.
If we consider, for example purposes:

level weight
TH9 4
TH10 3
TH11 2
TH12 1

ATTACK X DEFENSE (un: 1 star)
TH9 TH10 TH11 TH12
TH9 1 1,33 2 4
TH10 0,75 1 1,50 3
TH11 0,50 0,66 1 2
TH12 0,25 0,33 0,50 1

So if it happens an attack where a TH9 player gets 1 star over a TH12 he could earn 4 points.

*** consider that there can be no repeated stars ***

This could bring new considerations to a clan that relies solely on strenght like selecting only TH12 bases for the clan league. Is it worth to place our strongest bases? Will it hold TH10 and TH11 attacks? Can we always do the maximum score? Or should we go with a mixed team?
Regardless of the choice, the team will still depend on the ability of each player. After all, the chances of an attack from a TH9 base on a TH12 result in 1 star are still pretty small. But it will add a bit of fairness and maybe hope which is also good.

If you really read, this thread is not discussing about matchmaking. I think it should still be random within your clan league as it is.