Interesting thoughts here...
But one thing where I dont agree - I dont find the shorter masts more agile at all, on the contrary...
WHEN up and flying that is
As discussed in another thread, when you go down to say 70 or 80 cm it is not possible to ride as free and hard in carves, as with 90 or 100 cm masts.
Unless you will tolerate a slight touchdown of part of the board now and then - which is the crucial difference - I will never tolerate this, I will feel like a total failure if my board touches the water or wave ever so slightly even with just a small part
Some dont mind this, and might even have the board down ON the surface occasionally, when carving or riding waves, and then I can see the shorter masts might work really well indeed.
But if you dont want this (touching the water), the longer masts are by far more agile as you can lean harder and carve better with these
To the original question - yes it might be very different when surface riding, but as you are on an adventure and going towards more and more flying, you just have to take the slightly different surface riding into account - and enjoy the higher agility and carving ability and more fun in chop and waves, and riding higher, the longer masts will give you
The longer mast is not more difficult to balance either, when foiling.