If the question is referring to full range speakers meaning full range single driver speakers, some of the higher end Lowther drivers claim a 20Hz-20KHz frequency response. So I suppose they technically exist. Same for full range speaker "systems". So the question then becomes a measurement issue as whether or not every component in the audio chain can deliver the entire frequency range. If so, then theoretically there's no bottleneck.
The problem is if we mix the notion of the sound quality with measurements, then the discussion becomes completely subjective and there's no single answer to the original question.
The problem is if we mix the notion of the sound quality with measurements, then the discussion becomes completely subjective and there's no single answer to the original question.