Type of usage in this example

He fought hard for equality and workers’ rights, a rare quality of the times (noun phrase relates to the entire sentence)

How does this usage differ from a noun in apposition, in terms of recognizing what the phrase relates to clearly? Is this just a question of semantics and that the phrase just doesn't relate to any other specific word in the sentence that precedes it.

He fought hard for equality and workers’ rights, rare quality of the times

Is the determiner always needed in these instances as a rule? What is the difference with or without ?

Are the determiners in this instance (a) to stop it looking like the phrases isn't modfiying anything in the sentence?

Semantically it's the same meaning eitherway