I want the rules to be the same if you add a barbarian level to a troll or a human.
What do barbarian levels represent? Toughness. Some weapon training. A love of battle.
If I want my troll to be tougher, more loving of battle, and better trained in weapon use than its raw statblock would suggest, I can add these abilities in easily enough (eg make it elite and give it some sort of swordplay-modelling triggered action).
I don't want to be applying class levels which were designed for some completely different purpose, namely, building tough, weapon-trained, battle-loving
player characters.
I disagree vehemently that monsters shouldn't follow evolutionary patterns. It's a viable world that (while magical) should have an actual ecosystem.
I'm not remotely interested in evolutionary patterns, nor in ecosystems. I'm interested in myth and fantasy adventure.
A blacksmith should never be a minion. He's one of the "elite guard" in the town militia of a small village (because he's the toughest guy in the village) which means that he should be able to fight and not easily be killed by the first local kid throwing a stone.
Minion isn't an inworld status, it's a metagame status to be used in action resolution. Hit points are part of the same set of mechanics. Local kids throwing stones at NPC don't involve the action resolution mechanics, and doubly, therefore, don't do hp damage to anything.
Another advantage of this system is as you stated, the ability to remove special minion rules like "does not take damage on a miss". That's just another arbitrary 4E rule that doesn't necessarily make sense. Everyone else takes damage on a miss with a Fireball, but the minion is immune. Why?
Again, this is a metagame thing. Like anyone else, a minion suffers pain and burns from being caught in a fireball.
If a fireball is cast at 2 normal foes and 2 minions, and the GM describes the 2 normal foes suffering burns and the minions standing there unscathed, then something has gone wrong with the GM's descriptions.
This
could produce wonky outcomes, in the corner case in which a minion is caught in fireball after fireball, but the attacker never manages to hit, and so the minion survives blast after blast - the Rasputin of that particular battlefield. In practice, has this ever happened at anyone's table? And even if it did, it strikes me as a story opporunity as much as a problem - everyone else died in the battle, but this one schmuck managed to survive through sheer luck!
I don't know if that house cat is going to be a skill challenge or a combat challenge or a possible familiar or an ally for the druid or secretly a polymorphed archmage or whatever...until the rubber hits the road. This works against an improv-heavy game. I don't know what this housecat is going to have to do before I put it in the game. Once it's in the game, I'm going to need some way to figure out what happens to it, no matter what the players do to it.
This may be true, but I don't understand what it has to do with statting up housecats for combat.
If the housecat becomes a familiar, look up the stats in Arcane Power. If it is a skill challenge, use the DCs and damage rules from the DMG. If it is (in some bizarre way) a combat encounter, use the Wolf statblock and drop it from level 2 to level 1 (and narrate the bite as a claw instead).
Whatever one thinks of 4e's action resolution mechanics, it hardly has a shortage of them!
