I "basically" still use this concept.There was encounter design from the beginning.
The 1e DMG has a bunch of random encounter tables for lots of terrains, a system of categorizing monsters by monster level to factor into placement in dungeon levels, and suggested random encounter tables for various dungeon levels.
Check out for example page 174
DUNGEON RANDOM MONSTER LEVEL DETERMINATION MATRIX (d20)
Equivalent Level Of The Dungeon
Monster Level Table Which Must Be Consulted
I II III IV V VI VII VIII IX X
1st 1-16 17-19 20 — — — — — — —
2nd-3rd 1-12 13-16 17-18 19 20 — — — — —
4th 1-5 6-10 11-16 17-18 19 20 — — — —
5th 1-3 4-6 7-12 13-16 17-18 19 20 — — —
6th 1-2 3-4 5-6 7-12 13-16 17-18 19 20 — —
7th 1 2-3 4-5 6-10 11-14 15-16 17-18 19 20 —
8th 1 2 3-4 5-7 8-10 11-14 15-16 17-18 19 20
9th 1 2 3 4-5 6-8 9-12 13-15 16-17 18-19 20
10th-11th 1 2 3 4 5-6 7-9 10-12 13-16 17-19 20
12th-13th 1 2 3 4 5 6-7 8-9 10-12 13-18 19-20
14th-15th 1 2 3 4 5 6 7-8 9-11 12-17 18-20
16th & down 1 2 3 4 5 6 7 8-10 11-16 17-20
This gives a range of monster difficulties in an encounter to be expected that adjusts to the level of the dungeon. It gives a huge range of hitting anything from kobolds to spellcasting vampires at the deepest levels.
CR in 3e, monster level in 4e, and CR in 5e were tighter and used more directly and in smaller bands for suggested encounter parameters than in 1e monster levels, but AD&D had the concept as part of its rules.
Areas of the world have "levels" of danger, thereby granting a range I can choose from for planned encounters, or randomly roll.
Players know or are informed when entering dangerous areas.