In response to my comments on the material used for the arms on the Holybro Kopis 2 SE racing miniquad, this video explains a little more about how composites such as carbon fiber get their strength and why a foam/carbon layup may be as stiff as solid carbon but is nowhere near as strong.
Stay tuned for the ongoing testing of the Kopis 2 SE, the arms may not be solid carbon but they might well be "strong enough".