Shadorne...The off axis "lobing" which you cite is, in my experience, not a real world problem. Perhaps this is because the drivers flanking the tweeter are usually as close together as possible, (1 foot for the 7 inch drivers of my Madisound Odins) and have considerable surface area so that it is hard to say how far apart they are (acoustically). Furthermore, this lobing would occur for off axis listening in the vertical direction, where the off axis angle will not be large, and is easily minimized by tipping the speaker system. The effect is, however, why you should not generally use MTM speakers mounted horizontally.
Oh, and by the way, two driver speakers also exhibit lobing in the crossover frequency range where both drivers are active.