I wonder if the rigidity could be improved while staying modular, maybe just use many more screws? I don't mind undoing more than 5 screws for the bottom to come off, make it 20 and it's still totally fine.
IIRC from one of their videos, they mentioned that they deliberately use cast aluminium instead of CNC machined like the macbook. If they sacrifice build quality for sustainability deliberately, I don't see how they could compete with Apple.