That's a good point but it's the price you pay for having perm karma, it's simply the lesser of two evils everyone seems to think one system is perfect or the other is perfect or their idea is perfect, spoiler alert in this instance there is no right idea there is no perfect solution no one form of server fixes all the necessary problems while keeping regular players happy. It's purely opinion based as to which idea you're more for or against.
The price paid is the RDMer getting off without punishment while the actually players are punished, forced to play for up to a few hours (multiple map changes) simply to get back to having enough karma to be effective
The, as you say, lesser of the 2 evils is the RDMer getting banned quickly (1-3 rounds, one would expect), and actual player getting a karma penalty until the end of the map change. And during those 1-3 rounds, the person who rdms has the exact same karma he would have under the perm karma system. Meaning temp and perm karma punished minges equally, while perm karma severely punishes legitimate players who react the the guy mowing down other innos, leaving the temp karma system to temporarily nerf the legitimate players damage
As I see it, perm karma severely punishes player for shooting the guy that killed 3 people right in front of him, and not at all (Going from RDMing to a baiting is not a punishment. They can still do a good hit to karma, as is the intent.) the inno that killed the 3 randomly.