Exactly. I'm all for playing the NPCs with the stats and mental abilities they realistically should have. Shadowruns will tend to be balanced for the capabilties of the characters, but the wider world should be internally consistent - that mall security guard shouldn't suddenly have automatics: 6, nor should the Leopard Guards suddenly get gimped because the PCs decided to attack an Aztechnology facility out of the blue.
Back to the original question - melee is a niche role already, so be careful not to go overboard countering the PC. If he is using it all the time, then people firing from windows, or cover, or from a distance, should remind him that long range weapons are usually the better option to use. But a monofilament whip should be extremely effective when you can use it.
Some things to keep in mind, though. It is a distinctive (although easily hidden) weapon with the Forbidden legality code. Using one should get about the same reaction from law enforcement as using an assault rifle. It also makes a big mess (be sure to wear a poncho, or at least a bib, when using your monofilament whip
). Decapitated/dismembered bodies are a bit rarer than merely shot or stabbed ones. This could make the group easier to track, or even give them some Notoriety.
It is effective, but not at the top of the melee food chain - punching specialists, especially trolls and/or adepts, can do more damage, and two-weapon fighters with the right maneuvers will have a very dense defense (since two-weapon fighting gives you full defense with no cost of an action). And melee itself is not as common or versatile as ranged combat.
But someone using a monofilament whip, who is good with it,
should dominate most melee fights. Shadowrun is chock full of one-shot kills, so this is not unusual at all. I would worry less about it, and let the player have fun. Although I would still keep the reactions of the game world realistic.
