Really.. if you don't want to fix your @$!#, at least limit players to pings under 100. OR make servers dedicated to high-pings, if you really care about those.
But let's face it, there is a REASON those high-pings mostly use Phantom and you know it. Perhaps it's only a minority that is lag-switching, and the rest just choose to play on foreign servers, but they are not clueless about it, they all got the memo by now, they do it on purpose.
Lag should just not be an advantage. Period. Getting killed by katana should be aknowledged by the POV of the victim, not the one of the phantom. Katana shouldn't kill you if the phantom is 5 meters away. Yes, this system is the best for GUNS, but NOT FOR CLOSE COMBAT. Again, there is a reason fighting games require much lower pings to be playable. You made stabbing a key element for some mercs, thus you should disallow high-pings, or give them a dedicated server where everyone is high-ping.
But again, no need to fix this crap if you simply disallow high-ping players.
Oh and yes, there is another high-ping in that team and he wasn't phantom. You know why? Because he was lvl5 and hadn't received the memo about the exploit yet.