Precisely. If modern touch user interfaces are the result of any carefully-gathered metrics (a premise I find suspicious, but let's run with it), the metrics t

Precisely. If modern touch user interfaces are the result of any carefully-gathered metrics (a premise I find suspicious, but let's run with it), the metrics themselves must be orthogonal to the user actually being able to complete tasks in as short a time as possible. Efficiency, speed, and accuracy were the sort of metrics used in legacy UI design. But you are right, it's likely that modern metrics are things such as engagement, and whether the user is doing actions that are high-value for the company, such as sharing content with their social networks.