My definition of perfect? Are you having a laugh?
Going by your definition nothing can ever be perfect. Spring airgun is a mechanical object which is subject to forces, stress, strain etc. etc. If we look at details like bending of the compression tube due to offsets, almost every spring gun is subject to it, if the locking mechanism is not inline with the center of the piston/spring (and it never is on conventional springers).
As for the Whiscombe, if you want to analyse bending due to moment it's actually happening in both the vertical and horizontal planes (vertical due to what you said above) and horizontal as the gear is offset from the center of the piston/springs (it's below it), hence force is applied away from the place where the load is being held, bending the cylinder.
If we go into that much detail, maybe you'd expect airguns to be 100% efficient too, or anything less is not perfect...
Please define perfect