Many early Wharrams are very flexible vessels. This is in part due to design and also to lack of building and rigging finesse and lack of maintenance. Wharram's newer designs are lashed together. This technique applied with diligence and modern ropes will yield a much more rigid structure. Part of Wharram's design philosophy is that a minute amount of flexibility in the beam to hull connection serves to absorb the intense shock loading inherent at these connections. Indeed if you look at a boat with aluminum cross tubes it is very common to see stress cracks and repairs.
The open bridge deck boat certainly does leave a helmsman exposed, which over time in inclement weather can be both uncomfortable and dangerous. Much like many small monohulls.
On the Tiki 36 we addressed this issue by adding a windscreen and roll down curtain/windows for the helm station.