Disadvantages of a pretty boat?

Re the pinched stern, one advantage of this is that when the boat heels, the waterlines remain reasonably symmetrical fore and aft,hence she should still be fairly kind on the helm if the sails are balanced properly.
Contrast this with a 'modern' boat with a very wide transom - if she heels 20 degrees her immersed waterline has now changed a lot, and is very unsymmetrical fore and aft, hence she might have more of a tendency to 'round up' - while boats like the S & S 34 are very happy sailing at 20 degrees of heel, more modern boats prefer to sail more upright generally.

A modern boat with a wide transom will be more inclined to surf when sailing downwind - narrow IOR sterns are supposed to be a bit of a handful to steer when sailing downwind in stronger wind conditions, but the owners of the two S & S 34's that I know never seemed to have any problems here. And one of them has been around the world, while the other did an Atlantic circuit very happily (I crewed on the latter from St Maarten to Maine via Bermuda and Newport, and we had an excellent trip).
Maybe I am biased, but on my trip to Maine I used to disconnect the wind vane from steering while on watch and hand steer, as it was so much fun - ok, we never had more than perhaps 25 knots of wind, but even in those conditions we were stomping along with some reduction of sail area, beautifully balanced and with a very comfortable motion.

 

Sorry for the delay, when I answered your question the first time I was 20 hours into my day and wanting to get to bed. I finally got around to cleaning up my cludge of a spreadsheet for generating and analyzing sectional shapes wrt righting moment. And I found the parametric expression for one particular case. There is no constraint on hull symmetry for the wetted portion, so imagine the hull centerline lies at the waterline.



So here is the shape. It is shown upside down, but it represents the maximal first moment of area. I solved it numerically first, tried to run it through Euler Lagrange criteria, but unfortunately there were no ignorable variables to facilitate the integrations, and I had a nasty pair of nonlinear, nonintegrable, intergal - differential equations. So I went back to curve fitting, and eventually guessed the right family of curves and made the fit.

In the formula, theta goes from 0 to Pi/2