I have no idea what you wanted to show with your calculation above but if you’re saying you can’t cheat with weight than i think you need to go over your books again.
Let me explain this in a very simple way:
Rider X really weighs: 75KG
He rides Alpe du Zwift at 320W = 320W / 75KG = 4.26W/KG
Now since Rider X is a cheat he lowers his Zwift Body Weight to 65KG. Lowering his body weight in Zwift does not impact the power hes able to produce in real life but it has an impact on the Speed on Zwift…so again:
He rides Alpe du Zwift at 320W = 320W / 65KG = 4.92W/KG
Since hes lighter as a cheat and can produce more W/KG he will climb Alpe du Zwift much faster than real weight Rider X.