40 ghouls would be equal to 10 standard monsters, so twice the regular XP budget of 5 standard monsters. It's not that impossible.And that would be silly, and totally against encounter building. I've had a quick look in E2 and the most I could find was 10 ghouls (abyssal horde ghouls, level 26 ghouls... sigh) or 10 mercs (which I wonder where they found, these are identical mercenaries at level 24, rolls eyes).
It doesn't have to 'make sense' in the world. It's a game, it make sense in the game rules and that's all that matters.And he is still level 26, with defenses and attacks that make him deadly and invulnerable to characters at level 10 to 15 ? This is the part where it does not make sense, at least to me.
Except it's exactly the contrary, the rules of 4e dictate that you create minions of the appropriate level and create them for that purpose, so this is what drives your story. In 5e, I just decide that the story calls for a horde of orcs, I don't even have to look at the rules, I just use the orcs that I have, with the added bonus that they are not special bizarre orcs incredibly dangerous but very fragile, technically created out of the blue to satisfy arbitrary system constraints.
Those minions don't drive the story, they serve it? What exactly is so different between an Orc that dies to a single hit, except if you roll a 1 on your damage, or an Orc that dies in a single hit all the time? The Minions usually have different actions.