I think this is persuasive, and I like your barbarism/civilization division (paganism/Christianity being an aspect of this). It occurs to me that Shakespeare's other "classic" revenge tragedy, Titus Andronicus, which also raises acute problems of setting, shows civilization in transition to barbarism. This may not be coincidental.
The whole question of which historical markers writers and viewers/readers are going to be sensitive to is itself a historical question, and not a simple one because even within individual plays there's a lot of variation. On the previous post the point's been made that Shakespeare is more historically careful in representing elites than lower-class characters (clowns being especially likely to appear contemporary, to the point of breaking the fourth wall). Some effort may be made with the historical aspects of costumes and props, but little with language - that had to wait for Walter Scott. And, of course, not everyone's historical senses were in lock step: Jonson was far more pernickety than Shakespeare.
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The whole question of which historical markers writers and viewers/readers are going to be sensitive to is itself a historical question, and not a simple one because even within individual plays there's a lot of variation. On the previous post the point's been made that Shakespeare is more historically careful in representing elites than lower-class characters (clowns being especially likely to appear contemporary, to the point of breaking the fourth wall). Some effort may be made with the historical aspects of costumes and props, but little with language - that had to wait for Walter Scott. And, of course, not everyone's historical senses were in lock step: Jonson was far more pernickety than Shakespeare.