I'll get to the other points later, as for Murr merely "existing during Krayt's era" that does not mean that quote incapsulates him.
The quote says that Krayt possessed TK and Lightning that outstripped sith of his era. If it said he has powers greater than any sith during his time or in his era. It might incapsulate Muur. But as Muur establishes himself as a sith of a completely different time, he technically avoids inclusion to the quote.
For example the title King George of England, doesn't change because he visited Spain for a couple of months. The same applies to Muur.
Krayt himself is not of the Legacy era if we want to go into forced semantics here.
What I was saying was that Krayt was present during the empire era as well so you know, the idea that because Muur was born millennia ago somehow exempts him from the quote is clearly BS when Krayt himself is a person who wasn't born in the Legacy time.
He is not technically born during that time, but it is the period of time where he establishes most of his infamy and power. Which is why, Darth Krayt of the Legacy Era works. The same can not be said for Muur who established himself during the time of the exiles. And only exists as a spirit bound to a tallisman, during the Legacy era.