The cable may be a much better conductor than the human, but there will still be a proportionate current pass though the human. What matters is the proportion.
A simplistic analysis of just the human versus conductor. Some numbers stolen from this useful document. The bulk resistivity of a human is about 5Ωm, and you could say maybe 500Ω hand to foot. Copper is a vastly better conductor, resistivity of 1.7x10[sup]-8[/sup]Ωm. But even the heaviest lightning conductors are only about 5cm[sup]2[/sup], and start at about 1cm[sup]2[/sup]. So you get about 0.00004Ω over 1.5 metres at best, and maybe only 0.0002Ω at worst. Sounds good so far. Direct lightning strikes will deliver very significant current. 50% of strikes deliver over 28kA. So over the 1.5 metre gap from hand to ground, the voltage across the lightning conductor will be in the range roughly 1 to 6 volts. Which isn’t going to kill anything. Moving to the unusual strikes, you can get ten times that current in the last fraction of a percent of strikes, and that would see 10 to 60 volts, which does get you into the range where it might kill you. 50 V at the wrong moment will send your heart into fibrillation, so it isn’t to be ignored.
All of this depends upon the strike behaving like a simple Ohm’s Law problem, which it probably will not. The voltages involved can create all sorts of interesting and weird behaviours that mean the basic analysis is invalidated. It particularly needs the grounding system to be very well installed. If the ground is dry, or there is not a good very low resistance path in the ground, things get a lot nastier. One Ohm in the ground path and you have between 28kV and 200kV (50% of strikes) on your hand. That will kill you stone dead. Not heart stopped electrocuted (and revivable) dead, but irreversible large scale tissue damage dead. 100Ω in the ground (which could happen in very dry ground) and you will have a couple of million volts looking for a home. Then you don’t even want to be near the conductor.
Which brings up the issue of what the ground potential is. Where the lightning conductor enters the ground will be elevated to a seriously high potential. The potential difference with distance radially from the entry point can be many thousands or tens of thousands of volts per metre. Standing right next to a lightning conductor could cause you to be electrocuted via your legs. A hand on the conductor and feet even a small distance from the entry point in the ground will probably mean thousands of volts between your hand and feet - simply because of the voltage drop between the point on the ground where you stand and the actual conductor. Again, you won’t be electrocuted dead, you will be fried meat dead.
One further thing to think about - lighting conductors also get hot. They are designed for peak temperatures of 250C. That will cook your hand if you are holding onto it.