I'm an experienced drummer and I play regularly with, and without, click tracks; I can tell you that the assumption that "feel" or "groove" is only present when a drummer's time varies is not accurate.
There are at least two types of variation that matter in a drummer's performance: the overall sense of time and the moment by moment variations. The ability of a drummer to play a complete number and keep to a set tempo is really important, particularly in this day and age of digital editing. But it is a common feature of "click track performances" for the drummer to sway ahead of and fall behind of the beat (faster and slower). If done correctly this variance in tempo will add significant life to a performance and such a skill takes a lot of practice to perfect.
The subtle qualities of a drummer's performance go far beyond whether or not they stick to a given tempo for the duration of a number; this is just one variable that effects the quality of a performance. Some genres require a rigid sense (metal/electronica) of time whilst others benefit greatly from its absence (fusion/jazz).
Interesting software however ... I'm tempted to have a play with it.