You get 50% more completion XP from TW dungeons (compared to TWW normal) but you get 10% of the mob XP (at 71+).
The net effect is a normal TWW dungeon gives ~50% more total XP. People have run the numbers on this.
I didn’t buy TWW so all my characters can only go to level 70. Just today (10/23/24) I was in Pandaria with a level 70 doing pet battles and got ganked by a mob of level 71 rats. Like WTF Blizzard?!??!!? Is this the new “normal” where we can never go play in an old zone on easy mode because the whole game levels to the character?!?!? You certainly like to shoot yourself in the foot 
I’m soooo glad I cancelled my sub.