Man, that scene between Luthen and Saw was SO INTERESTING.
Because we don't know a lot about Luthen, much like Saw, but we DO know more about Saw, just like Luthen seems to. The audience isn't aligned with one character or the other necessarily, we can go back and forth a little.
Luthen's lack of explained backstory, the fact that he's always putting up some kind of act, some kind of front, means that we as the audience don't really know him either. It's hard to know exactly what he stands for and what his plans are with Cassian. He's not affiliated with Saw, he isn't explicitly affiliated with Bail Organa yet, and he's not affiliated with any of the other known organizations we've been given in mainstream Star Wars before (the Separatist/Republic divide from TCW). All we know is that he SEEMS to be anti-Imperial. But one of the last people we were told was pretty firmly anti-Imperial turned out to just be out for himself.
And on the other hand, we DO know Saw. We know his origins on Onderon and the death of his sister. We know just how long he's been fighting oppression of his people. We know what he does and what he becomes in the future. We know that he's willing to do some pretty heinous things in the name of his cause, but also that he's one of the only people aware that the Death Star is something that needs to be figured out and is trying to track it down to keep it from becoming the problem it has the capacity to become. We know Saw. The good, the sympathetic, and the ugly.
So it's interesting to see this conversation with Luthen, Luthen who says "we need a little extra oppression in order to actually spark a real rebellion," which seems ruthless enough to fall in line with Saw's own tactics, except that Saw's not willing to risk his own people, his own cause, for someone else's mission. He's unwilling to help someone else if there isn't something about it that helps his personal agenda.
And we also see Luthen refuse to pick a side beyond bringing down the Empire, arguing that they can do more together than they can separately, and that their infighting can wait until the Empire's been taken down. Saw's choices to protect his own people for his own agenda go against all of his big talk about how everyone chooses a side but he's the only one really fighting for the galaxy. Saw's more inclined to let petty infighting keep him from helping other people in favor of just trying to do everything himself and assuming he can do it all himself. Which isn't unsympathetic when absolutely no one listens to him later about the Death Star, so in some ways he's not WRONG that if he wants something done he just needs to do it himself.
We don't know who Luthen is really, we don't know why he does what he does and makes the choices we see him make, which makes him inherently untrustworthy but also leaves the option open for him to surprise us with his alliances. We do know who Saw is and why he does what he does, which means even if we don't LIKE him, we can trust that we know what choices he'll make. We can trust that we know where he stands.
Saw stands at the front with his people, he's hiding out in cold caves with his people and making absolutely no bones about who he is and what he believes. He's got nothing to hide from anyone.
Luthen stands behind all of his recruits, letting them do the work while he stays on Coruscant in relative safety drumming up support from senators to fund his efforts and just passing information where it needs to go. He's hiding from everyone.
This scene was incredible because so much went unsaid and lives in just... the audience understanding who Saw is as a character and how that juxtaposes with the relative little of what we known of Luthen.
Which seems like such a wonderful way to use a legacy character, to take the fact that this character has been around for a while and that most audience members will know him and his story, to compare against a character who is completely new and unexplored. That dynamic that the audience has with the characters has been transposed into the dynamic the characters have with EACH OTHER and defines the place they currently hold in the narrative and its themes. It's masterful.