Yes he was weaker.
The difference between a Vampire Spawn (a minion) and a Vampire Lord is not cosmetic. They are not interchangeable. Neither in combat or in the lore of the world. A Vampire Spawn is a once living humanoid that has been blood drained by a Vampire Lord. Vampire Lords are much more powerful immortal undead, that would never be confused with a spawn. The difference between them is *not* decided by the arrow shot by a PC. They have separate ecology in the world, and so do even weaker minions like Kobold Minions in relation to Dragonshields.
Sure, I grant you this case. A vampire's spawn are supposed to be weaker, and they are usually easy to tell - any seasoned vampire hunter can tell vampire from spawn.
But I think that's a small exception to my general theory.
Think of a bar scene in one of those
Steven Seagal movies where he beats the crap out of everyone there on his way up to the villain on the other side. None of those ‘thugs’ are a challenge or even threat to him, no matter how many times he fights them. They are not going down in one punch or kick because he got lucky, or critical hit them

, but because they are weak and nothing compared against the skill of Steven. He is always going to bend their arm backward and break it and make them scream, “You *)$#, you broke my arm!” Because he is just that awesome and they are just that pathetic.
I would not call this minion vs. non-minion.
In your Steven Seagall movies, I see it as a high level fighter (Seagall is certainly paragon, and in many of his movies, could even be borderline epic) enters a room full of low level fighters (mostly all level 1 with a possible few exceptions of level 2, 3, or maybe a rare level 4).
He wipes the floor with these guys because their attacks are weak (need a 20 to even hit him, and Seagall has tons of HP and healing surges, while he can hit them with anything but a natural 1).
Because they are low level, they don't have many HP, and Seagall is dishing out lots of damage, so they die or are rendered unconscious (or disabled, as with breaking arms).
Even Seagall is known to hit these mooks with combinations, striking them several times to bring down a mook. Other mooks he one-shots, maybe using stuff that 4e might call encounter powers, or maybe just good rolls with his at-wills...
Then he gets upstairs and finds the boss, and the boss' trusted henchmen, and these guys are higher level. High enough level to make a fight out of it. They damage Seagall, and he often has to damge them multiple times to kill them.
But here's where it gets into Minion Land - Seagall can one-shot some of these high-level henchmen, and often does. Especially in those movies where he uses guns or blades.
The difference?
Some of the bad guys in the upstairs floor are high level fighters, some are high level minions.
Which all fits into my theory outlined in my previous posts.
It’s the same idea with Minions in 4e.
Yes, the same as I just oulined here.
Kobold Minions die in droves to PC’s because they are nothing to the heroes. They are peons even among their own kind.
I disagree.
Among their own kind, a kobold minion may be a little weaker than a kobold specialist, but that's only a matter of training. As for their HP, they are both kobolds. If a kobold minion picks a fight with a kobold non-minion, they will be hacking and swinging and wrestling and probably even biting each other bloody, until one gives up or dies (or the other kobolds break it up). Maybe that non-minion has some special training that makes him more deadly in the fight, gives him an edge, but otherwise they are virtually identical.
Until the PCs bust into their lair and one-shot the minions and have to three- or four-shot the non-minions.
Just like the thugs in the bar in the movie are peons that are probably ordered and beat up earlier in the movie by the main bad dude or his right hand man, in order to foreshadow their own threat level.
Nah, just really low level bad guys.
If you or I broke into that bar and picked a fight, we probably wouldn't one-shot any of them, and would get our butts handed to us right quick.
(You're not Steven Seagall, or Jet Li, or some other super tough martial artist guy are you? If you are, then you might beat up that bar room of low-level guys too. I still wouldn't).
Now eventually Seagal comes up against the fat bodyguard or the muscled henchman that protects the villain and he gets a real fight, and this is the same as PC’s coming up against the Brutes or Soldiers or real threats in an encounter. Those foes are never going to be one-shotted, because they are the bigger kahunas not just in the battle, but in the larger game world itself. It’s a pecking order.
As I said above, these are the high level guys that put up a fight, but some of them might still be minions.
These guys, even the minions, can hit Seagall. They can hurt him. They often do. (Well, Seagall doesn't get hurt as much as Bruce Willis, aka John McClane, but sometimes he gets hurt).
Seagall kills/disables some of these guys quickly, in one or two shots (high level minions), but others take a long protracted fight scene, many blows exchanged, blood flowing on both sides, until eventually Seagall prevails (high level non-minions).
It all fits perfectly into my minion-world-view.