It seems like the design would simply *have* to be easier in a following
sea.

Absolutely NO and a little bit yes !

Consider that there is LESS reserve bouyancy in a pinched stern. So,
in a steep following sea the sharp stern will initially penetrate into
the following wave as the wave advances ..... in contrast to the
fat-ass boat that lifts more/faster initially (and by reaction puts her
bow deeper into the trough).

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Supposedly, more Perry double-ended designs (mostly Tayanas and
Valiants) have circumnavigated than any other 'production' built /
designed sailboat. Thats pretty good 'testimonial' on a stern design
thats based primarily on Bob Perry's asthetic/styling whims. As I
stated on another post, Perry will flatly state that his tumblehome
canoe stern is totally design 'style' ...... His canoe stern designs
in comparsion to other 'double-enders' have more (although limited)
reserve buoyancy incorporated into his 'bustle' at the waterline.
There is a very big difference in the shape of Perry's canoe sterns and
other designers 'double enders'.

IMHO Where a pinched stern has advantage is when forced onto an extreme
heel. Then, the symmetry of the double-ender hull form can heel at
great angles ***without affecting change in weather/lee helm
balance***. Like an inland lake scow, you can sail a Perry design
'double-ender' over onto its beam ends and have very little change in
helm balance. Also note that the max. beam in such Perry designs is
carried quite full for the majority of the hull plan; hence, the less
than 'ideal' windward performance. .... always a trade-off.