Maybe it's better not to buy into this discussion, but...bugger it, why not!
We're only talking, fellas and girls, not buying and selling sheep stations.
Lu, I'm inclined to agree with your reasoning regarding the loss of lift when the blade is aligned with the longitudinal axis, although I'd call it a reduction rather than a total loss.
Also, there is probably a disruption when it passes over the rear cabin and tailboom area, where the downwash would be deflected and the induced flow would, I imagine, be decreased. The exhaust airflow must have an effect too.
All in all, the blades experience various different states of relative airflow all round the disc, so no wonder they flap up and down like crazy (just look at that footage from the 'Chopper' series, or whatever it was called, where a camera was attached looking outwards from the hub of a huey inflight, makes you wonder how the damn things stay on for 1 hour, let alone thousands!).
Naturally then, all the forces generated by this movement will be transferred to the transmission mounts, which will absorb and damp it.