But some monsters are strong against certain builds and weak against others.
That sounds like a party composition problem, then. Don't everyone play ice mages and then walk into a volcano.
Some monsters are stronger in certain environment and entirely nullified by others.
Sounds like monster creation rules need to be figured out before publishing the books, then.
Some monsters are stronger given certain allies and weaker when alone.
Again, monster creation rules should be reliable. And they shouldn't include context buffs that absolutely wreck the power curve.