Wing flex on modern aircraft makes them safer, not weaker

Modern airliner wings are deliberately designed to flex up to several metres during flight — on a Boeing 787, the wingtips can bend upward by about 7 metres. This flexibility absorbs turbulence loads, reducing stress on the airframe and saving weight compared to a rigid wing that would need to be far heavier. Rigid wings would crack under the cyclical stresses of thousands of flights.

Source: Boeing 787 Airplane Characteristics for Airport Planning (2017); FAA Advisory Circular AC 25.571