Not P but Moby-Dick (11)

[Mike Jing]

The following excerpt is from Chapter 34:

Wherefore this difference? A problem? Perhaps not. To have been Belshazzar,
King of Babylon; and to have been Belshazzar, not haughtily but
courteously, therein certainly must have been some touch of mundane
grandeur. But he who in the rightly regal and intelligent spirit presides
over his own private dinner-table of invited guests, that man’s
unchallenged power and dominion of individual influence for the time; that
man’s royalty of state transcends Belshazzar’s, for Belshazzar was not the
greatest.

First, what does "To have been Belshazzar, King of Babylon" indicate? Is it
a wish, or something else entirely?

Second, in the last sentence, are "that man’s unchallenged power and
dominion of individual influence for the time" and "that man’s royalty of
state" in parallel? Melville’s liberal use of the semicolon is confusing
sometimes.