Yeah my 'naturally-locked' 80 seems so underwhelming, even with max-upgraded Hero gear, which isn't far from the tier of stuff we used for 70s. My guess is that since DF had a bonus season that jumped iLvs higher, that gave us a little golden age and Midnight scaling might not ever be that good with how far TWW iLv got. =\
TWW made a massive design error. I'm not even sure it was intentional. It may just be that whoever was doing it had no idea how anything worked. It was so bad that there's a nonzero chance that's true.
By DF S4 it had rained Veteran gear so nobody should've been below ilvl 480. Serious players were 500+. Even 490+ wasn't that hard. That was at level 70.
For reasons I cannot fathom, TWW was tuned to a MUCH lower ilvl. Just based on the drops, TWW dungeons dropped ilvl 408 at level 70. At the exact same time, a level 70 DF dungeon drop was still ilvl 467 (which was S4 Adventurer 1/8)..
So it's standard Blizzard scaling to get weaker as you level. It's always particularly bad in the last 5 levels before max level, which just feels horrible. So 70s were strong with the scaling naturally PLUS they were 100 ilvls higher than the content was tuned for.
Defenders of this argued that Blizzard tuned things for what ilvl you'd be if you levelled through DF and hit 70 at probably ilvl 400, not 480+ like you were in S4, but I don't think that makes sense. SL didn't have that problem. BFA is harder to gauge because there was an ilvl squish going into SL.
But it got worse: initially Bismuth boxes dropped gear with no level minimum and those were ilvl 545 so you could get a level 70 in full 545 gear. This got fixed a week or two in.
This problem was so bad that a few days in Blizzard did an across the board 70-79 nerf that made everything in dungeons in particular feel horrible and 75-79 was already horrible.
AND 70-80required more than twice the XP that 60-70 did in DF while the XP rewards for dungeons and quests remained pretty much exactly the same.
As an altoholic I levelled only one toon in TWW from 10. It was an Earthen. I levelled a bunch in Remix and honestly won't level outside of Remix in Midnight. I didn't even buy Midnight.