I appreciate your answer but if +100 points in a graph represent a 2/1 ratio (i.e., "twice") then -100 points would represent a 1/2 ratio (i.e., "one half"). If your distro is twice faster on test A, but the other distro is twice faster regarding test B then, on average, both distros have the same performance. This is the precisely the result obtained if you take the average of +100 and -100, which is zero. However, taking the average on your misleading graphs we obtain (100% - 50%)/2 = 25% giving the false impression that your distro is a 25% faster on the average, when the truth is that both distros have the same average performance (i.e. your distro is 0% faster).
The problem here is that you are mixing a percentage (i.e. a relative value) with a baseline (i.e., a reference for an absolute value).
You do not need misleading graphs for seeing improvements or regressions. Your misleading graphs will be only giving a false appearance of performance in cases where is none.
Now I think you're confused. The average of "half as fast" and "twice as fast" is not "neutral" in any math that I can think of (before my morning coffee at least)