It might actually be linear — how minds actually function is in many cases demonstrably different to how it feels like to the mind doing the functioning — but it doesn't feel like it is linear.
The technology doesn't yet exist to measure the facts that generate the feelings to determine whether the feelings do or don't differ from those facts.
Nobody even knows where, specifically, qualia exist in order to be able to direct technological advancement in that area.
It might actually be linear — how minds actually function is in many cases demonstrably different to how it feels like to the mind doing the functioning — but it doesn't feel like it is linear.