So let's get back to the method of using medium strength commercial (non-aerospace certified) aluminum 6061-T6 angle... and let's discuss the method of using "bent angles" instead of extrusions.
Using these angles to make a truss fuselage is not perfect, because obviously the angle has a lower buckling threshold than a tube.
BUT this is easily and reliably able to be calculated and quantified using very standard and accepted methods. The appropriate adjustment (to address the difference in buckling) can easily made to allow this. So (random example) instead of bending the L-angle from .025 aluminum sheet maybe it has to be .032 in certain places.
Being able to make an airplane fuselage out of less expensive non-aerospace material is a worthwhile goal, but it still needs to be consistent, predictable and reliable.
There is more than way to skin a ship (tennie two) :
And this Russian Argo build in aluminium angles :