What component is responsible for dynamics ?

Raya,
You state a very rational explanation for the obvious advantage for high efficiency speakers. This also has been my own experience.
Best Regards,

The more sensitive the speaker the more likely the noise floor will be higher, and the softer end of the dynamic scale will more likely to be negatively affected.

Unsound I must say that has`nt been the case for me, but to each their own. What ever works best then go for it.

Watts are cheap, high powered SS amps with medium efficiency full range speakers can produce impressive dynamics.

High efficiency speakers will raise the noise floor, same with cheap tube equipment.

Without a very large enclosure, high efficiency speakers will lack low end due to Hoffman's Iron Law.

Bookshelf or limited LF speakers lack the necessary low end impact needed.

Yes, Unsound, your last post doesn't make alot of sense to me, either. High efficiency speakers, especially horns but also other types, are well known for very high quality at the very softest dynamics. This is one huge reason why so many professionals prefer them. I have never found noise floor to be higher in high efficiency speakers, quite the opposite in fact.