It’s especially noticeable with Essence of Evil (and Trick or Treat) because the tooltip of “All Status Effects” STILL says “Impervious troops will only be Cursed” when the behavior was explicitly changed to apply Curse first (thus bypassing Impervious entirely).
It’s also hard to define “simultaneous” on a technical level, i.e. if one effect changes based on the outcome of another (such as in this case Silence bypassing Alert via Stun) then by definition this is NOT “simultaneous”.
The only logical definition of “simultaneous” I can think of is similar to the definition of “concurrency” used in databases and “commutative” in mathematics: the end result is the same regardless of the actual order applied. Meaning each effect is processed on a separate (internal) copy of the target data, obliviously to other effects, and the results are combined. The difficult part is how that final step can be … complicated.