B4: The Lost City is a classic module for D&D. At one point it (in)famously stops giving full description of the rooms but instead lists monsters in each area and tells the DM to figure out why they're here themselves. Once the reprint will show up in new anthology, I'm sure people who complain online whenever WotC uses "ruling not rules" or "DM decides" or "these parts were left for the DM to fill in" in their design (and then continues buying WotC books to keep bitching and doesn't touch 3rd party or other games for some reason) is going to be normal about it. /s
But some monsters are strong against certain builds and weak against others. Some monsters are stronger in certain environment and entirely nullified by others. Some monsters are stronger given certain allies and weaker when alone.
If you could devise a system to assign monster complexity based on every scenario you can imagine that monster being part of, then either that's an astonishingly small number of scenarios or an absurdly complex calculation to force on anyone.
Bullshit man. Pathfinder 2e had incredibly tight math behind it's design and very simple ways for dms to use it, dnd could easily do the same. Especially since dnd's direction seems to be about giving as little mechanical choice to the players as possible.
They could make a program where you give it the players' character sheets and the encounter and it simulates a bunch of battles to see how they do. But failing that, you could make CR be a good average, where you could just look at that and adjust based on what the strengths and weaknesses are. I haven't actually played 5e so I don't know this from personal experience, but my impression is that they haven't done that. Some creatures just don't have a CR that matches them in general.
There's also no system for figuring out the CR of an encounter with an arbitrary set of monsters and enemies with class levels.
That sounds like a party composition problem, then. Don't everyone play ice mages and then walk into a volcano.
Sounds like monster creation rules need to be figured out before publishing the books, then.
Again, monster creation rules should be reliable. And they shouldn't include context buffs that absolutely wreck the power curve.