You are right, 3 is the mathematical ratio of omni versus cardioid sound power. But I did not say that conventional speakers were exactly omni, I said, they were approaching it. At 250 Hz speakers like Genelec 8030, Neumann KH120 or Kef R3 (for coaxial) are pretty close to omnidirectional (DI≈1dB).
This is a big difference (cardioid has DI≈4.8dB) in a frequency range where early reflections and sound power dominate the sound pressure level a listener is perceiving, and this will change the tonal balance significantly, all by reducing the reflected sound in the room. With increasing frequency the effect decreases and at about 800Hz the difference is all but gone.
However, from the manufacturer data it seems as if the Orbit has some extra narrowing around 1.5kHz, so the effect might go up a little bit higher in this case.
So, we are on the same page, I guess.
As for the cancellation when going off axis, I do not exactly understand the geometry of the situation.
In a room there is so much reflection that mids (at least) should be everywhere.
At 90° off axis a cardioid has approximately 6dB level decrease (lower mids, highs will decrease a bit more). So there should still be the full signal, just softer, a bit darker and with bass emphasis as the Orbit's bass is omni.
Where exactly were the ears placed? I cannot say anything about this case.