Ive had no trouble either with the wing joints. The single large screw is not uncommon to hold on even up to >30 pound aerobatic planes. The wing tube is taking the loads and the screw would have to strip or break and/or the ply mounting crutch would have to snap off to allow the wing to let go. Not likely! Try pulling a 6mm screw out of a threded Tnut or coupler some time, it is well over a thousand pounds force.

I also bash my reaper (split S's and inverted, regular loops) around and it has developed no play in the wing mounting area.

AJC