You are missing the fundamentals of physics, mainly that every force has an equal reaction force, unless that body is in motion. In the case of an engine, that bouncing is reacted by the wing. If it wasn't, the engine wouldn't stay attached. Albiet that pylon to wing attachments are pretty complex, every force, dynamic oscillation, thrust, reverse thrust and torque must be reacted by something. Most pylons use point loading attachments to transfer those forces. The forces those points transmit are definitely cyclical, and those attachments must be fatigue resistant.
I've been thinking about this for about a day now (ok I did break for sleep and work and stuff
and I figured out why it didn't sound completely right, and yet not completely wrong.
Here are my thoughts: All forces from the engine and pylon must be transferred to the wing but this does not have to happen all at once. The function of the pylon assembly is thus to flop around and slowly transfer energy. If it could be transferred all at once we might as well have a rigid pylon/wing interface, which would have to be much heavier and stronger.
Same thing with the wings. They flap so that their energy is transferred slowly to the fuse (and, incidentally, the engines). Energy is retained in the flapping motion. As the flapping decreases, the energy is slowly transferred to the fuse.
This is like the suspension in a car. It stores energy so that it can be transferred gently to the car instead of just passing along every little bump in the road.
So yes, the force are of course transferred, but the pylon mounting shields the wings from the worst of the forces. Flopping about of the engine is a sort of energy storage. The energy is stored so that it can slowly leech to the wing.
Or I may have it all wrong
But I'm sure someone here has a degree in physics!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo