I agree with most of your points on this one
But I think that the disadvantages far outweighs the few "performance" advantages (at least for me)
The very reason we are so much better on the water than windsurfers, are (IMO) the fact that we can outbalance everything by means of an efficient powerstroke.
Meaning, we get on a plane so much faster, and can stop and start whenever we want to "on the dime" - precisely because we dont have to bear too much away and get apparent wind and "rely" on this only
Windsurfers are extremely inefficient on short tracks, because they have to bear away and use a long distance to get into planing, compared to a kitesurfer that can use the kite instead, OR use both bearing away and the kite - so here we excel over any windsurfer.
When going downwind, deep (racing f.ex), or when jibing with any board - we can also use the "dynamic" range we obtain by having the window to position the kite and get the powerstroke at the EXACT point we want it, and in a reasonable amount
(the latter is the problem if too short lines - the amount is not satisfactory....)
Especially in waves, you would most often like to be able to get some kitepower, even when you are standing still trying to conquer a breaking wave and heading upwind to get angular over it - so here apparent speed wind does not make sense at all (not an option).
And when riding waves, you would never rely on apparent wind directly - but would search for the best line through the surf and curl etc - so here you would both like to have short lines for quick direction change yes - but longer lines to be able to have some power reserve in every situation.
At least my personal experiences were, that 15-20m lines are the shortest I like to use in waves.
And 15 or 17m are too short for me most of the time, so I use a bit longer always, so I dont have to change but can get to know my setup better instead
But it is clear - that lines has become shorter over the years.
20-24m is standard line length on most kites today, as a good compromise between what we want.
Many years ago 27-28m was used, but history now