Your statblock is not absolute in any real way. It changes all the time. There's an entire leveling system that changes your statblock routinely. Never minding things like level drain, magical/mundane enhancements, situational modifiers, etc.
One thing that doesn't change your statblock, however, is the foe you're currently facing.
Sure, various foes might impose temporary penalties, but your underlying statblock stays put.
And mechanical symmetry is a myth. It's certainly mythical in AD&D. What is the wisdom score of an orc? How much experience does a dragon have? How, exactly, does an orc suddenly gain a boatload of HP, Strength and attack bonuses the second he becomes a chief? What if that orc chief is young or old? On and on.
Easy on all counts: all you have to do is extrapolate the PC rules and apply them to monsters. 3e's implementation of this was wonky as hell but the underlying principle was rock solid.
What's the wisdom score of an Orc? Roll 3d6 and apply racial modifier. An Orc becoming a chieftain just means it's got a few levels under its belt. They shold IMO all get their Strength bonuses in combat, their Con bonuses to h.p. and applicable saves, and so on.
As for dragon experience, the only time I need to know its class level (and thus its general xp range) is if it's a caster; as it casts as if its (usually MU) level.
Statblocks are an abstraction of a snapshot in time. Your statblock might be X right now, but, tomorrow, it might be Y. And, again, 4e D&D was very clear on the notion that the mechanics were absolutely NOT meant to be used if the PC's were not present. If you're applying cats to minions, that's your fault for not using the system as written or intended.
4e might have been clear on it but I still think it's a terrible approach. The setting exists when the PCs are not present exactly the same as when they are.
Never minding that in AD&D, an ogre can have 5 HP.
As written, yes. But if you give said Ogre the Con bonus to its hit points that it should have, that 5 minimum suddenly becomes 25 minimum (Ogres having an average Con of about 18).
Looks like a minion to me. Let's not forget, as well, that a 1st level fighter can kill an AD&D ogre in one round without too much difficulty. Weapon Specs and a longsword is 28 points of damage in a single round. More than enough to kill most ogres. Add on a percentile strength and now Mr. 1st Level Fighter can quite reasonably kill an ogre in a single round.
How are you arriving at 28 points from a F-1 in a single round? Its max on the die is 12, +3 for double-spec, which comes to 15. Where's the other 13 points coming from? (even maxed-out 18.00 Strength only gives 6 more points o' hurt)
Now a two-handed sword could get closer - max roll is 18, again +3 for double-spec, gets to 21 - but that still ain't 28.
