When the aircraft is level both blades provide equal thrust.
The increased thrust of the downgoing blade compared to the upgoing is a phenomenon that occurs when the a/c is in a climb..
The definition of "critical engine" can be found in the literature, loosely defined (by me) as being the engine the loss of which will provide the pilot with the greatest amount of difficulty in controlling the a/c under the most adverse circumstances i.e. high temp., high alt., high weight, a/c loaded to CofG limits.
When level the yaw and therefore roll tendency exists because of the greater distance from the longitudinal axis of, in this case, the downgoing blade of the left engine.