I appreciate the thought to determine how much amps the motor is pulling in peak conditions but surely, there is more to this calculation than by implementing a homemade rolling road.
There is more, but it gives a baseline as an example. It's not taking into account other factors which could swing things in either direction.
I don't deny that a fixed mass would have an impact on riding uphill (such as if someone is riding fully kitted or with a spare battery etc). But bodytype vary between rider to rider. As such body weight will vary as well. Not to mention that someone who is perceived to be heavier, may be proportionate in conjunction with their body type (ectomorph, endomorph and mesomorph).
I don't think if someone is "perceived" to be heavier or not is the argument

If someone is heavier, they're heavier. If they're lighter, they're lighter.
The heavier a mass, the more energy required to lift it against gravity.
In this case, that can come from the battery or the rider.
The weight of the bike is inconsequential as the bike will have to lift it's own weight no matter what the rider weighs.
A light person will require less energy to get them up the hill than a heavy person. If the heavy person can compensate for their own additional mass with their fitness and strength, then yes, they could possibly achieve the same height/distance as the lighter person. However, for the cyclists body to be efficient when climbing it will need strong legs and as little unnecessary other bits as possible. Tour de France riders for example, don't look like they play darts in the off season.
Equally, where you have Biathlons, where people ski and shoot, you never see Cibiathlons where people cycle as fast as possible, then stop, swig 4 pints of beer and try to get 180 on a darts board before moving off to the next beer/board. (Though arguably, you could have cycling pub crawls which might be similar, but none competitive).