looking at the level ranges to see progression/scaling for all levels.
classic : desolace, southern barrens, hinterlands, arathi highlands and both stranglethorns are now 10-30. interesting that the rest of the zones are just 15-30, not spread out like before. and they scale up to 30, even though 25 is the new 60.
tbc : spread out from 10-30 to 25-30
wotlk : spread out from 10-30 to 25-30
cata : all 30-35 including tol barad
mop : leveling zones spread out from 10-35 to 30-35. isle of thunder flat 35 and timeless isle 30-35, not sure if its an oversight.
wod : leveling zones spread out from 10-40 to 35-40. tanaan jungle flat 40. ashran doesnt state level requirement
legion : all leveling zones 10-45. suramar, broken shore, argus flat 45
bfa : leveling zones spread out from 10-50 to 35-50. mechagon and nazjatar flat 50