This is revisionist history. Old school D&D explicitly had balanced encounters, and called them dungeon levels. Each level lower you had progressively more difficult encounters. Challenge ratings were introduced in 3rd Edition along with the 'Back to the Dungeon' motto, and just tied it to party level instead of dungeon level. You also had published modules indicating the total number of party levels that are appropriate and which character classes are necessary to complete it.b) No Challenge Ratings or Balanced Encounters, though warnings of dire things ahead are acceptable