Well let me ask why it's better to set your MM to a specific flick distance? That's the thing - they are all arbitrary. There is no objective way to prove that one flick point is better than another. It is all subjective preference, as you said. However, what we do know is that if one point on the monitor is matched then the rest of the screen will be unmatched. Therefore we can make some conclusions about the advantages and disadvantages of different percentages.
Let's say you match at the crosshair (0%). We should expect to have very good tracking, micro-adjustments, and feel much more in control of our aim as we turn and approach a target. But the consequence of matching at the center means that muscle memory will get much worse as we deviate from the crosshair. This is why extremely high FOVs are much too fast to control and extremely low FOVs feel too slow in comparison (as you approach 180 FOV the cm/360 becomes 0). However, this is more of a problem of distortion than a reason to not use 0%. All percentages have problems at the extreme FOV range but they are not reasons to prefer one percentage over another.
Now since the higher percentages are arbitrary, I am not going to assume any particular percentage. But we do know, in comparison to 0%, that we should have much greater overall muscle memory. This is because the sensitivity doesn't start at 0cm/360 at 180 FOV (infinitely fast). It's a much more evenly distributed range of sensitivities. These are some old crappy charts I created but it shows how the cm/360 for different methods eventually converge as they approach 0 FOV:
You can even test this in the calculator.
So in contrast to 0%, the higher the percentage, the less matched the crosshair becomes. This is very important to consider because that means that as we approach our target from our match point we are going to be increasingly less in control.
You must realize that we do not complete flicks in one single movement. We are constantly making adjustments as we approach our target. This is why it is more important to have the crosshair matched because we want to make sure we are in control when we are on top of the target, because there is no point in acquiring the target only to find we cannot stay on top of it due to our muscle memory being whack.
One interesting phenomena that happens when you test all this out is that at higher FOVs it feels like you have more control with a higher percentage. However, this is not the case. You must make sure to differentiate between matching points on the monitor and the sensitivity simply being slower. A decrease in sensitivity may feel like you are in more control but you are not doing yourself any favours when it comes to muscle memory. Just consider how low FOV would be perceived - a higher percentage will feel much too fast at the crosshair. You are going about it the wrong way.
It's very important that we make this distinction. We must choose the percentage according to its advantage, not because it feels better at [X] FOV. Ignore distortion. Distortion will be there for every FOV.
So if we compare the advantages of using 0% to a higher percentage, you will realize that there really is no reason to use anything other than 0%. Especially because it isn't arbitrary. It translates the same no matter what setup you are using. It's not like having better overall muscle memory helps much. It's still not perfect. You are going to have to learn slightly different muscle memory for every different FOV no matter what percentage you use. You could alleviate this problem by using the same FOV in every game you play but then what would be the point in converting sensitivity?
0% is the point on the monitor where the 2D world and the 3D world touch. It is the tangent to the curve, the true idea of "viewspeed".