I finally got in with my team and ran Temple of the Jade Serpent at level 80. I recorded a video and it should be available sometime tomorrow, if not Wednesday, but here is my initial experience.

Difficulty:
As everyone has said so far, mobs definitely take more time to kill, but I don't think they do much more damage (no idea if that was even buffed). If I had to estimate, and I do because I don't have hard numbers from before 7.3.5 for TotJS, I'd say that each boss took, at least, 5x longer to kill.

Reward:
I hit level 80 last night with this 5-man team, so my characters couldn't have had more than 1-5% of experience before starting the dungeon. After completing the dungeon, I only had 74% of level 80, and after turning in both of the quests in TotJS, I still only had ~94% of level 80. So, I didn't even gain one level, with the 300% RaF benefits. At this time, I do not envy anyone leveling without RaF.

Another quick example from WaDaFruCK in the ISBoxer Discord:

Abominations in Stratholme (Live) had 110,000 health, and he was doing 700 damage per character. So, 110K HP / 3,500 Damage (all 5 characters) would take 31 spell casts, per character, to kill the thing.

As others have been discussing, this scaling feels unnecessarily over-tuned.