So still curious, I did a bit of further checking. Here's what Kreia has to say:
"And its empire, the true Sith Empire, rules elsewhere. And Revan knew the true war was not against the Republic. It waits for us beyond the Outer Rim. And he has gone to fight it in his own way".
I think the loadscreens are more of a general guide than anything to be relied on with accuracy. Further, those loadscreens also operate on the same knowledge that the PC has. To the galaxy at-large, the true Sith appear dead. That doesn't mean they actually are, even if that was probably the intent of the K1 devs. Clearly, K2 retconned this.
I'd be wary of what Kreia says. Remember, she manipulates you for the entire game. It's really only at the end that she finally comes clean as to her true motives. Your second point is interesting, but more of a plot hole than anything else. When it comes down to forecasting what unknown enemy Obsidian intended Revan to face, I think it's clear that the True Sith were that enemy. In addition to the dialogue in-game, devs have confirmed this was the case.
But at the end of the day it's your mod. You include whatever you like!