Unfortunately, because this was a Living Campaign, there was no common denominator at all. There was no way to expect one for your typical convention session.
That's exactly what I mean. They can't be tailored to a group. They have to be shipped out the door in one of two states: 1) Dumbed down to the point where any group can do them, regardless of make-up; or 2) Built for the expected party. This is writing towards the lowest common denominator.
If the group is standard make up, (1) becomes trivial and boring, while (2) is fun.
If the group is a nonstandard make-up, depending on what skills you have available, (1) is going to vary between boring and mediocre, and (2) will shift madly between completely trivial and insanely deadly.
Part of 3e's encounter design advice includes encounters that are very difficult but become easier if you have a particular key to that encounter - some tactic available to the PCs that makes it a lot easier. But they're supposed to be a small proportion of the encounters. Using them too often, particularly because the event cannot control for the makeup of the table, should be considered bad encounter design.
You're proving my point, which is that you were far more constrained in encounter design in 3e than you are in 4e by what classes are going to play the adventure. I haven't played much 4e, but I haven't noticed, for example, a case where simply including certain monsters makes a cleric-less group lose bowel control at the gaming table. That was standard operating procedure in 3e. And don't get me started on parties without a full arcane caster. You just don't run published adventures above maybe 3rd level without one, IME.
So, the fundamental rules of 3e created a very large space of encounter design that would be considered "bad" by the definition you're espousing. This space includes assuming the party has access to magic above 3rd level, assuming the party can detect magical traps, assuming the party has any meaningful healing or restoration effects, and so on. That's a lot of "bad encounter design."
You don't think that maybe, just maybe, rather than an epic possibility space of "bad encounter design" that kind of severe restriction might reflect a more fundamental limitation in the game?
I chose the word limitation here deliberately, rather than "problem." It's not necessarily "bad" to strongly encourage certain classes. But don't try to claim that it's less limiting than 4e.
For example, if we're making a party in 4e, someone is going to say, "We need someone who can heal." And in the core books alone (all I have experience with in 4e), I can find both the cleric and the warlord, and neither of them is going to cause the rest of the table to groan and throw a book at my head. Whereas in 3e, if faced with the same question, I rolled a cleric. Full stop. Or I took a book to the forehead. Rolling something else might have been more fun for me, but everyone at the table remembered those encounters that ate us alive last time we used a druid rather than a cleric to heal.
This is where you accuse my DM of sucking for not adjusting for the limits of the party. He ran published adventures by the book. Lots of people do that. It's what most new people do at least for a while. It's what they have to design for. If you have a DM who is willing to go under the hood and convert that standard Detroit model to run on vegetable oil, hydrogen cells, or a Mister Fusion, that's great. It removes restrictions of many kinds. But in 4e that kind of thing is merely tinkering because no single class is carrying literally game-changing effects in its pockets. In 3e it was massive overhaul, depending on what classes were missing.