I think this is overly reductive. Speed (or more likely, perceived speed) is only one part of UX, and how much it matters depends a lot on what else is going o

I think this is overly reductive. Speed (or more likely, perceived speed) is only one part of UX, and how much it matters depends a lot on what else is going on and the users expectation. Even focusing merely on responsiveness feels a bit superficial. Something a bit closer to the core of it is that whenever a user is focused on waiting for your software, it reduces their experience. That can be articulated better I'm sure - and still is only one part of the (complex) equation.