Thinking about the place of minions in the game reminded me of this from 1e. I thought it was by DMG combat tables, but it is on page 25 of PHB under the table about fighter, paladin, and ranger attacks per melee round (that increase from 1 to 3/2 to 2 as they level):
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Granted that melee rounds were one minute in AD&D because it "is not in the best interests of an adventure game, however to delve too deeply into cut and thrust, parry and riposte" and instead the "system assumes much activity during the course of each round". (DMG page 61). Still, a 20th level fighter getting 10x as many attacks against a 0-level (or d7 or less) monster than against a 1st level (or d8 or higher) monster shows how big of a difference that 1st level is.
I somehow knew the rule existed, but I have no recollection of fighters always (after1st level) taking multiple attacks against Goblins (d7) and Kobolds (d4). I wonder if that comes from starting with B/X and if those who started with 1e always did (and also used a lot of the combat rules in the DMG I don't remember).