"unless designed otherwise" is a pretty powerful escape clause. I mean, unless designed otherwise, every building is the Chrysler Building in Manhattan, no?
What I would say instead is, it's simplest and easiest to construct a ribbon microphone as a figure-8, and specific acoustical adaptations are required if you want to obtain any other pattern.
However, those can be quite successful. I once owned a pair of Beyer M 160 hypercardioids, and if there hadn't been severe RFI problems with them (they put out ~1/10 the signal levels of condenser microphones and by their basic design, are highly responsive to magnetic fields), I think I could have kept them around for a while. For relatively close-miked vocals, sometimes you don't want too high a degree of detail. But in general the high frequency response of ribbon figure-8s is severely restricted, e.g. 10 or 11 kHz seems to be the general upper limit, above which they roll off significantly. There's a reason why the heyday of ribbon microphones ended when FM broadcasting began. (I could get into talking about nostalgia, World War II vs. the 1950s and 60s, and Bing Crosby vs. Frank Sinatra ...)
Condenser figure-8s are better, but as far as high-frequency response is concerned they're the worst among condensers; single-diaphragm condenser figure-8s typically go only about 1/3 octave higher up than the best ribbons, and that's restrictive enough for me! Unless they use built-in equalization like Sennheiser's do--but then that can be applied to any figure-8. Or unless they create the figure-8 pattern by facing one cardioid forward, and subtracting another, rear-facing cardioid from it (or adding in inverse polarity); that can work--Neumann and Sennheiser have both offered small-diaphragm, multi-pattern microphones that have worked that way.