I feel for you Tom, it should have been addressed a long time ago, and personally I can't understand why this has not been done. It must be the biggest gripes within CCs.
It is very frustrating to create a tourny for lower tiers only to look and see the leader is a legend - I quit one CC because of this as the owner did not want to step on anyones toes. Sadly the lower tier members then will not bother to participate when it should be fun for all levels.
Consider running a handicap tourny, a bit of work but can be done well (we have one running currently and I have been nudged into second place by a hack lol so they can work).
And i agree (in fact great idea) that the leaderboards should be concealed in premium tournys (perhaps a sign up period like RGs) as if someone shoots a really low score it will deter others entering