Does Old School RuneScape play well one-handed?

Reposting with more detail after my last thread got no traction. It behaves as expected on one account and not on another, same device.

Corrections welcome, especially if I got a detail wrong.

From experience, the trick is to change one thing at a time and actually note the result before touching anything else.

For what it is worth, measure before and after, otherwise you are just guessing whether it helped.