I think the suggestion about lapped cars not going offline to defend is the most sensible. That is something that can be regulated. The one grey area could be whether the car being lapped is trying to pass someone ahead, but if you simply state they can’t even go offline for that pass, it’s still less obtrusive than the current rules. It also allows the leaders to not be artificially hampered, yet still requires a degree of skill in dealing with backmarkers.
I will say this in regards to all the complaints that it’s “not fair” to the leaders to be slowed by traffic. It’s equally not fair to the cars lower down to sacrifice their race for the leaders. “Punishing” them for being slow by making them go slower does not improve the racing. We already have people complaining that the lower teams are so slow, yet people are calling for them to bend over backwards and go slower to let others by. And frankly, it’s a circuit not a beginning-and-end course. The fact that you run into lapped traffic is part of racing on circuits inherently. If you think it shouldn’t be, then mayhaps it’s time you switched to rallying.