I agree that the trigger on a double action revolver should not be eased forward during the normal use of the revolver. However, when I am examining a revolver, I consider easing the trigger forward to be a valid test of mechanical function.
If slowly releasing the trigger causes the trigger to stop before reaching full reset, then I think the revolver has a mechanical issue. Usually the problem is that the return spring is too weak, but sometimes the problem is friction or mechanical interference.
Whenever I change springs in a Smith & Wesson revolver, I slowly test the trigger to be certain that it will fully reset in all circumstances. I also include this test in my examination of revolvers that have exceptionally light double action triggers.
If the trigger always resets in rapid double action, but sometimes fails to reset when the trigger is released slowly, then I do not have confidence in the revolver. In my mind, I do not feel confident that the revolver will always work correctly because the trigger will be released rapidly during use. Instead, I feel that the revolver is giving me an early warning about a mechanical issue that has not yet caused a failure, but is a little too close to its acceptable tolerances.