I think leaving a roulette just because you don't like the location it selected goes against the spirit of the roulette system. How about locking people out of using roulette for a longer period if they do this, but still letting them use Duty Finder the normal way to pick their favourite dungeons?

Obviously this would be unpopular as the main reason people opt for roulette in the first place is for those bonus rewards, but the purpose of the system is to keep the queue active for people who actually need to do specific content. It's not doing them any favours if half the party leaves on entry because the penalty for doing so is outweighed by the potential rewards of running faster/better content a short time later. If they're leaving because they think they will make more exp/tomestones per hour by doing so even with the current penalty, the system needs to be adjusted to discourage this behaviour.