But every user is in many ways non-average.
Thus if you create a system tailored at the average user, then none of your users will be happy.
This is objectively true. There's an excellent 99PI about exactly this: https://99percentinvisible.org/episode/on-average/
> Thus if you create a system tailored at the average user, then none of your users will be happy.
This is objectively false. Some users will find some frustration or unhappiness with certain things, but remarkably, there are plenty of software UIs that get the job done for just about everyone.