Their behavior in the time domain does not suck. These Quads are among the most time coherent on the planet, as you can tell by the impulse response and its ability to reproduce a square wave.
Now all panel speakers other then the Quads beam like crazy. Peter Walker reasoned that if you place a tight polythene membrane across a room and produce sounds one side, it is perfectly reproduce on the other.
Now the membrane does not move as a whole. It moves like ripples on a pond, with time delays as you move from the center.
This is the genius of these speakers, he reproduced this effect by the "archery target" delays built into the speaker.
The signals are progressively delayed, but the resulting wave form is not! It is highly coherent!
The only deviation in the time domains is related to stored energy in the membrane in the upper frequencies. You can see that in John Atkinson's measurements.
Your statement comes from individuals who do not understand the principle of operation of these speakers. If what you stated was correct, then they would not stand a prayer of reproducing that square wave if free air.
That is why a speaker with fourth order filters turns a square wave into a pretty perfect sine wave. That is time distortion with a vengeance.
The THD of the Quads is 0.1% THD. This is better than most tube amps, and equal to the best of them.
A lot of us including myself have spent a life time trying to get the quality and transparency of Perter Walker's Quad speakers. In fact I think it is fair to say that his throwing down of this benchmark, has contributed more to the improvement of moving coil loudspeakers than anything else.
I know that is what I aim for and do not play fast and loose with phase and time, as you can see from the impulse response of my speakers. I'm glad to say they sound an awful lot like Quad ESLs with more dynamic range and bass extension. For small intimate recordings I want my speakers to sound as close to the Quad's as possible.
I have to give great credit to Peter Walker for giving us the distant lofty target to aim for.