single versus multiple driver?

A driver large enough to produce low frequencies has too much mass to allow for the quick movement needed to produce higher frequencies. That's why a single driver is not used, except in things like portable radios. Devices that use a single driver will be compromised too much in either high or low frequencies relative to a good multi-driver design. Otherwise, everybody would be making them.

cone drivers are usually not as linear as electrostatic drivers, ribbons or planar magnetic drivers.

so the question should include these drivers as well.
i believe cones are flawed, whether one or several.
cabinets and crossovers do not help either.

it surprises me that there are so few panel designs commercially available.

given your musical preferences, you may be disappointed.

Consider active speakers. There is no crossover and less IMD from the complex interaction of multiple drivers all connected to one amp. Tannoys have active dual concentric speakers if you are concerned about point source.

Larger fullranges can produce deep bass. So many only have experance with very small drivers that could never aproach fullrange but folks still call them such. Face it 4 1/2in driver can not be fullrange;) That being said a good fullrange loudspeaker in proper cabinet design can produce very deep detailed bass and quality trebile but it will not be cheap. Many manufacters offer the small comprimised so called fullranges in wee AS boxes.Sure they can sound fine in small room or nearfield but they dont show what a true fullrange realy can do. That being said I perfer compresion drivers in multiway systems very costly to do right. Dont over look fullranges with super tweeters or bass drivers or other loudspeaker designs you can have it all if loudspeakers designed right but most are major comprimises designed for profits, WAF,trends or shipping costs as much as performance.