What is the meaning of 之 and 当 in the phrase "比之当初战火蔓延的速度有过之而无不及"?

Question

The sentence looks like this:

乱葬岗大围剿刚刚结束，未及第二日，这个消息便插翅一般飞遍了整个修真界，比之当初战火蔓延的速度有过之而无不及。

I do not understand the meaning of 之 here and also do not know how to read 当 in this context (and what is the meaning of it here). Is it dang4 or dang1 in this case? What does it mean? Is it a separate word here or part of 当初, because I even not sure how to separate 当初战火 into separate words because I can't figure out the role of 当 here. I would be grateful if anyone could be able to explain this in the manner that I would be able to use similar sentence pattern in the future myself. As of now I'm out of ideas after a long time of research.

Answer 1

之 is acting like a pronoun for the first statement here

[A] = [乱葬岗大围剿刚刚结束，未及第二日，这个消息便插翅一般飞遍了整个修真界]

[比] = [(verb): compare]

[之] = [(pronounce for) [A]: it]

[to] (implied)

[B] = [当初战火蔓延的速度]

[有过之而无不及] = [conclusion]

This sentences are comparing 'the speed it spread' of [A] to [B] and the conclusion is [有过之而无不及] (can only be faster, not slower)

[A] [比] [之] (to) [B] + [conclusion]

[A] [compare] [it] (to) [B] + [conclusion]

A shorter example:

[A] = [違者 (the ones who violate the rule)]

[B] = [斬 (execute)]

違者斬(之) = the ones who violate the rule, execute (him)

之 here is a acting like a pronounce "him" for 違者

I said 之 is acting like a pronounce because it is also acting like a preposition 'to' for the verb

"違者斬(之)" can be interpreted as "(to) execute the ones who violate the rule"

You can omit '之' and say "違者斬", just like you can omit 'to' and say "execute the ones who violate the rule"

Answer 2

乱葬岗: a burial hill, people might hide here in time of war, thinking no one would look there

插翅一般 stick on wings the same = like it grew wings

比之 compare to 当初 then

比 之 当初
compare to then = like before

有过之而无不及
better than and not worse than

乱葬岗大围剿刚刚结束，
They just finished surrounding the burial hillock and,

未及第二日，
not even waiting until the day was over,

这个消息便插翅一般飞遍了整个修真界，
this news took wing and flew around the whole of Xiuzhenjie (a town??),

比之当初
(just) like before

战火蔓延的速度有过之而无不及。
it spread faster than the speed of the war itself.