Biggest down side to penalising clans for playing below their account strength, is that it will hurt the lesser skilled players/clans that will naturally play below their weight.
Therefore, it would be much better to use rewards to promote effort instead. Make it so that under performing is simply unprofitable.
That way, the only heavier rosters to be seen in the lower levels would be those that need the extra weight in order to compete, rather than sandbaggers.
Equilibrium can be achieved, but not until the medal system is constructed in such a way that effort on the playing side is required in order to gain sufficient rewards.
In my view, the unweighted ladder should allow for "actual fair" matches, whereby more skilled players will give up "weight" to lesser skilled ones.
But medals are dictating the system, so that is where the catalyst is. Push to promote positive action and growth, rather than penalising inaction. Think positives as a solution, rather than negatives in order to try and dissuade.