I am confused.

RT70 means Road to 70, it's a buff on certain servers that gives you increased xp gains until you reach level 70. NoRT70 means you can't use that buff.

Yeah, and functionally the Road to 70 buff means that you don't have to optimize for experience gain and leveling - simply completing MSQ (incl. running the required story dungeons) brings you well beyond level 50, without the level gating and dungeon grind you'd otherwise have to face without RT70. So it both makes the routing simpler and brings the overall run duration down to a more manageable level (though still quite lengthy) for a single segment run.