Not sure I agree with this statement. Cassandra said that the world could only take so much change and that Justinia knew this, unlike Leliana. So there's that. Then again it probably boils down to their different perception of Justinia. Both would probably like to think that their views aligned with hers more, but there is no way to know who is right, without actually asking Justinia. But I only read the books until Asunder, so maybe other ones provide more insight on that, idk. As for Leliana conversation, I have to admit I didn't pay any attention after "Waaa I'm glad you're not the one who chooses the Divine" part.
Again, this goes back to Cassandra having no idea who Justinia really was. Justinia didn't know those things and clearly worked in opposition to this, even in Asunder. The fact is, if you asked me if Justinia is more like Cassandra, who had a very loose business relationship with her, one that Cassandra by your own words admits gave no insight into Justinia's character, or Leliana who might as well have been her daughter, I'm going with Leliana. This is like saying there is no way to know if Abraham Lincoln really wanted to ease the South back into the US instead of setting up the military districts that came later. He clearly did.
It happens when you say that the templars were bribed, so you can visit your home? I only recall Josephine saying something like "They're lucky Cassandra didn't know". What does this have to do with her bending the rules? But I only saw this convo once, so maybe I'm missing some detail here.
The Divine cannot legally have lovers or marry, I'm not sure what's so confusing about this. So no, Cassandra is probably not going to take the Inquisitor on as a lover when Chantry law forbids it. As opposed to Leliana who says **** it, and tells everyone she's banging the Warden, and then later saying, "And now it's okay too."