The laws of physics dictate that, after the spark starts, the current flowing in the secondary circuit and the voltage at the plug tip are determined by, among other things, the resistance of the resistor in the plug. (The secondary coil has resistance as well.)
The voltage of the secondary circuit is primarily determined by the rate of collapse of the magnetic field of the primary circuit. This might be Faraday's law. I forget. Its part of the reason that point gap & condition is important.
I think spark voltage is around 20,000 volts but might be as high as 40,000 volts. If the primary side draws 10 amps (guess, I'm not sure what the real figure is) then the secondary current will be 0.003 to 0.006 A.
Using V=IR if the plug resistance is 5 k Ohm, then the voltage drop due to the resistor will be 5000 * 0.006 = 30 volts. Hardly significant.
I think plug performance is about the insulator and its integrity. I suspect that plug resistance might just be a metric of insulator condition.
The resistor is there for suppression of radio interference. So, I think its real job is to damp some of the transient voltage spikes that surround the main spark voltage.
Here is a bit of an explanation by NGK
PLUG STUDIO / NGK