You forgot about spruce (Spruce Goose for instance) It was and still is used today to build airframes for experimentals( Flybaby and others) and ultralights ( Minimax and others). The only thing plywood is used for is mainly gussets and firewalls and some skin areas. Poplar and fir are commly used today too. The poplar is about the same weight and strength as spruce. Fir is a little heavier.
If a wooden plane can be built very light, and to withstand the fast hard jolts of rough landings, vibes from engines and props, and being bounced around in turbulance, then with some skill and knowledge, I see no reason a strong, reliable MB couldn't be built with wood.