I'll take a stab:
I imagine this largely comes down to anchoring stat blocks as precise descriptions of the creatures they represent. Wolves are like so, so changing one of their properties to produce different gameplay undermines their role. You have not defeated a real wolf, instead the wolf was modified to allow you to defeat it. Comparison to other wolves is thus invalidated, and the fantasy you're trying to deliver doesn't happen, because instead of the character demonstrating something about themselves, they've taken advantage of a property of the opponent, and worse, a property that was induced specifically for them to do so.
I'm less confident in the appeal here, but I think it's about the origin of the mechanics? The AD&D mechanic is a property of the character, instead of a property of the monster.
Appreciate the answer. Going to work backwards:
1) The AD&D original instantiation of this was both (a) a property of the character (you chose Fighter class and the mechanics afford a specific exception when faced with extremely low HD creatures) and (b) a property of the monster (their HD value being less than one d8 HD), so we've got a pretty big (and relevant) confounder to your proposed hypothesis.
2) So thoughts on the first paragraph:
A
wolf (or any monster) wouldn't have been modified to allow you to defeat it. They actually wouldn't have been "modified" at all, but rather
created using the monster building rules. But if we want to just stay with "modified" for these purposes, that's fine because that isn't the point of what we're discussing. The wolf would have been modified in order to (i) generate a particular fiction while simultaneously (ii) generating a particular, intra-challenge dynamic that either respects (i) or dovetails with it. Now, post-scene, the situation might mature and later we might need to actually modify an NPC; an easy use-case is that you rescue an NPC Minion from certain death, they tag-along, and downstream they mature into an actual Companion Character.
Here is an example of the above. This is a 1st level Minion NPC named Bita-Bousseh. She was a barrister for a covert group in the Empire the game is taking place. The PCs were entangled with that group early and wanted her allegiance. That meant her survival in an early conflict. She was just a vulnerable, Tiefling barrister of a covert group at that point so her statistical debut related (a) that fictional positioning and (b) provided a foundational element for a compelling tactical Win Con of "Keep the (Minion) Barrister Alive." Here are initial stats in that conflict:
Bita-Bouseh
Medium natural humanoid, tiefling
Level 2 Minion
HP 1; a missed attack never damages a minion. Initiative Minotaurs
AC 16, Fortitude 13, Reflex 14, Will 15 Perception+5 Speed 6
Standard Actions
Infernal Glower
Attack: Ranged 5 (one creature); +5 vs. Will
Effect: The target cannot attack Bita-Bouseh until the end of her next turn.
There Will Be Order
Immediate Reaction (Encounter)
Trigger: Bita-Bouseh or an ally within 3 squares of Bita-Bouseh is knocked unconscious.
Effect: Bita-Bouseh or the ally heals 1d6 HP and saves against 1 ongoing effect.
Lawyer's Dodge
Move Action (Encounter)
Effect: Bita-Bouseh shifts 3 squares and can shift through difficult terrain until the end of her next turn.
Languages Common, Supernal
Skills Athletics +3
8 levels later, here are her stats as a full-fledged Companion Character (or cohort or follower in alternative parlance):
Bita-Bousseh
Medium natural humanoid, tiefling
Level 8 Controller (Leader) XP 300
HP 59, Bloodied 29, Surge 14, Surges per day 8; Initiative +6
AC 23, Fortitude 20, Reflex 20, Will 22 Perception+6, Low-light vision
Speed 6
Resist 9 Fire (5 + 1/2 L)
Standard Actions
Infernal Glower (At-Will), Fear
Ranged 10, Target: one or two creatures
Attack: +11 vs Will
Hit: 1d8 +9 damage, and Bita-Bousseh slides the target 3 squares.
Bedevil the Fray (Recharge 6)
Minor Action - Ranged 5
Target: 1 ally
Effect: Bita-Bousseh slides the target 3 squares, and they make a melee basic attack as a free action against an adjacent enemy.
Infernal Wrath (Recharge 4,5,6), Fire
Free Action Close burst 10
Trigger: An enemy within 10 squares of her hits Bita-Bousseh.
Target: The triggering enemy in the burst
Effect: The target takes 1d6 +7 fire damage, and the target grants combat
advantage until the end of its next turn.
There Will Be Order
Immediate Reaction (Encounter)
Trigger: Bita-Bousseh or an ally within 5 squares of Bita-Bousseh is bloodied
or knocked unconscious.
Effect: Bita-Bousseh or the ally spends a healing surge and gains an additional
1d6 hit points and saves against 1 effect that a save can end and shifts 3
squares, ignoring difficult terrain.
Lawyer's Dodge
Move Action (Encounter)
Effect: Bita-Bousseh shifts 3 squares and can shift through difficult terrain
until the end of her next turn.
Languages Common, Supernal
Skills Acrobatics +6 (Escape), Bluff +13, Insight +11, Stealth +8
S 11 (+4) D 14 (+6) W 14 (+6)
C 12 (+5) I 16 (+7) C 14 (+6)
Fiction has accreted around her over the course of the Heroic Tier of play, but/and (not sure which here) the fact that she was a Minion in her opening scene and is a fully realized Companion Character later doesn't undermine anything (not their role, not their fiction, etc). If anything, I suspect the players might say
it backstops it.
We didn't have a concern about "another Tiefling barrister of a covert group" entering play and the minion rules undermining anything (fiction, immersion, etc). And, to date, that lack of concern hasn't proven foolhardy.
Another Minion used in that game were mindless
CAIPHON PLASMAS which would carry out their rote work of horrifying undulations and whispers in the name of their dread imperator. They had a move action called Flowing Slime that let them shift half their speed and a standard action called Psychic Slam that afflicted psychic damage and vulnerability psychic. They were small rivulets of The Dread Star Caiphon itself, born into the world from a vile Warlock nexus into that alien celestial body. There was a nested Skill Challenge to
Disrupt the Caiphon Nexus. Until that was completed, you had these dangerous spawns of Caiphon entering and threatening this world (and the PCs in this scene). And you had the Warlock and his own summonings to deal with.
But the Caiphon plasmas had their fictional place and had their synergistic mechanical instantiation. We didn't have a concern about "Caiphon Plasmas" later entering play and the minion rules undermining anything (fiction, immersion, etc). And, to date, that lack of concern hasn't proven foolhardy.
Same goes for the
Stone Spider Broodlings that saw onscreen time not long ago. Same goes for several other Minions. I believe people are saying its a problem for them, but its just not clear to me what people are imagining happening in the play of the game that would generate this state of "undermining" that is being proposed.