In that case, I probably have been very lucky to have acquired a very different genus of Semul. It is not flaky at all and sands rather well into a white finish. The feel is very similar to balsa but is about 2.5 times heavier.
I have used simul wood to make all parts including the bulk heads for boats and sheeted them with plastic sheets (for my Antares / Naughty Cal Cruiser build).
However, with its weight factor it may not be suitable for serious aeromodelling. I have crafted fuselages for small chuck / catapult gliders out of it and they flew satisfactorily.
That could be the variety/trunk portion wood that is much denser and used in making Match Sticks.
As you have already testified, Semul is not apt for Aeromodeling where Weight so Critical. Boats/Trains/Static modeling is are much more forgiving.
There is another wood used by cheaper Kits in India called 'Japanica' or 'Punjab Pine' which was exactly same problems and are much brittle.
Advent of EPO/Depron has been such a bliss for the Hobby!!