Why are electric bikes ranked on torque ratings? A major ranking criterion for electric bikes is the torque rating of the motor.
Generally speaking, bikes/motors with higher torques are sold at a higher price than bikes/motors with lower torques.
As a follow-up of this thread, I get that having a bigger torque helps in torque intensive situations, like hill climbing.
However torque can easily be multiplied/demultiplied using gears between the wheel axis and the motor axis. For example, these gears can be dedicated (embedded in the motor itself) or in the transmission system of the bike.
So the torque that matters is the final torque on the wheel axis, not the torque output on the motor axis.
So, this implies two questions:

Use of dedicated gears to change output torque: Why is torque rating sold as a discriminatory constant of the  bike (especially for the price), where it's easy to just add a gear on the motor itself to increase the torque, at the cost of increased RPMs of the motor axis (as it's done on electric cars)?
Effect of the transmission system on the motor torque: Since motors can be hub motors or mid-drive motors, the motor is not at the same transmission step: meaning the same motor output torque will not have the same impact on the wheel torque.
For example, a hub motor with a torque of 50 Nm will provide a final torque of 50 Nm to the wheel. However, a mid-drive motor with a torque of 50 Nm, with a gear ratio of 0.5, will provide a final torque of 25 Nm to the wheels.
With this in mind, how to interpret the advertised torque for a bike with a mid-drive hub, since it's heavily dependant on the transmission?
Addressing just the actual question as stated to avoid a 3,000 word essay:

With this in mind, how to interpret the advertised torque for a bike with a mid-drive hub, since it's heavily dependant on the transmission?

The advertised torque on a mid-drive bike will tell you over how large a band of cadences and how steep a hill the bike can actually provide the advertised assist level in watts.  (generally 250W equivalent mechanical rider input at the crank.)
A low torque bosch active line motor might only provide 250W of equivalent mechanical input assistance at exactly 70rpm on flat ground, whereas a Performance CX can provide that assist level at much lower cadences and on much steeper inclines.  The manufacturers try to reduce this to a simple number because it's consumer marketing.  (and also the drive system manufacturers don't sell you a final assembled bike, so they don't know what final numbers will be at the drive wheel in the installed system.)
The marketing is targeted to consumers buying finished bicycles made out of mass market bicycle parts.  In reality the transmission is always going to go from a bit over 1:1 to around 36:11 to 38:11 and the drive wheel will always be about 26&quot; to 29&quot; outer diameter, these things aren't just infinitely variable to get whatever outcome you want.
Certainly if it were all made out of infinitely ideal &quot;high school physics&quot; components you could use any combination of motors and gearings to get any torque number you like, but these things have to be made out of real materials that don't strip teeth or snap in half or overheat when spinning at the speeds that people's legs actually turn, so there are a lot of engineering compromises to be made.