Agree that the variable time is the biggest concern. Since "The shortest time was 1.5 ms, the longest was 4.5 ms. The mean ± SD was 3.4 ± 1.3 ms." I did a few calculations using that overall range.
Recall that Distance = Speed multiplied by time
So, if the ball is traveling 1 meter per second you get:
1 m/s * (0.0015 to 0.0045 sec) = 0.0015 to 0.0045 meters = 1.5 to 4.5 mm... or a variation of 3 mm (which is 0.118 inches)
[For reference 1 m/s = 3.6 km/hr or 2.24 miles per hour)
Put into common terms, if the ball is traveling at 1 meter per second after you press the flipper button the the ball will travel anywhere between 1.5 and 4.5 mm before the flipper acts... and that won't be consistent... one flip will be only 1.5 mm, one will be 4.5 mm, one will be 2.2 mm, ...
You also need to think about the following conditions:
* Trapped ball - very slow
But still.. variable time or response will result in your aim being off
* Ball rolling through inlane - generally moderately slow
Variable time or response will result in your aim being even more off
* Ball coming straight at flipper (for a live catch or drop catch) - from slow to very fast
Variable time or response will result in not being able to catch or control the ball consistently
Now let's turn the above into real speeds based upon https://pinside.com/pinball/forum/topic/how-fast-does-a-pinball-travel and http://tiltforums.com/t/maximum-ball-speed/2334/20
--> about 10-15 mph after a flip (but that seems to be contested)
--> generally 5 mph?
--> about 3-4 mph in general?
--> about 2.3 mph after a flip
(15 mph = 6.71 m/s) * (1.5 to 4.5 ms) = (10.1 to 30.2 mm) --> variation of 20.1 mm or 0.792 inches
(10 mph = 4.47 m/s) * (1.5 to 4.5 ms) = (6.7 to 20.1 mm) --> variation of 13.4 mm or 0.528 inches
(5 mph = 2.24 m/s) * (1.5 to 4.5 ms) = (3.4 to 10.1 mm) --> variation of 6.7 mm or 0.264 inches
(4 mph = 1.79 m/s) * (1.5 to 4.5 ms) = (2.7 to 8.0 mm) --> variation of 5.4 mm or 0.211 inches
(3 mph = 1.34 m/s) * (1.5 to 4.5 ms) = (2.0 to 6.0 mm) --> variation of 4.0 mm or 0.158 inches
(2.24 mph = 1.00 m/s) * (1.5 to 4.5 ms) = (1.5 to 4.5 mm) --> variation of 3.0 mm or 0.118 inches
(2 mph = 0.89 m/s) * (1.5 to 4.5 ms) = (1.3 to 4.0 mm) --> variation of 2.7 mm or 0.106 inches
(1 mph = 0.45 m/s) * (1.5 to 4.5 ms) = (0.7 to 2.0 mm) --> variation of 1.3 mm or 0.053 inches
So even at a very slow speed of 1 mph or 0.45 m/s the impact is >1 mm
and it is a dramatic 4 to 7 mm for typical ball speeds.
This seems very significant to me...