Analysis:

1. The speakers need to move fast enough to reproduce the sound. When you play a music with only 3 instruments plus a vocal, the unified wave is not very complex. Even you play it in a high volume, the bookshelf speaker with only one tweeter and one woofer could handle it clearly.
2. However when you play a symphony, you would have to handle a very complex unified wave. It means that the speaker has to move very quickly in a dramatically way jumping from one frequency to another in a very short time. If at the same time you play it in a high volume, the speaker may not have enough time to jump quickly from one frequency to another while the cone is at its further position to its middle location.
3. For floorstanding speakers, the workload is spread among more drivers. That means each driver is working at a half volume if you have double number of drivers than the bookshelf speaker. At a lower volume, the speakers handle the complex wave very well.
4. I call the less crowd/busy music as less frequency-dynamic music since it has smaller amount of notes. The crowd/busy music is high frequency-dynamic music since it has larger amount to notes.
5. I call the music with dramatic changing volume as volume-dynamic music.

Conclusion:

1. Good quality bookshelf speakers (with a sub) can play as well as the floorstanding speakers in a low to medium volume most of the time for most types of music. They also work well in home theatre setup because many workload go to centre/sub/surround speakers.
2. Good quality bookshelf speakers (with a sub) can also handle volume-dynamic music in a high volume to some degree.
3. Ggood quality bookshelf speakers may still struggle to reproduce frequency-dynamic music in high volume.
4. Good quality floorstanding speakers are needed to handle frequency-dynamic music in high volume.

Just my two cents. I might made some mistakes to comment on something which I am still learning.