Gravity I/II should be changed so that immunity to movement speed reduction does not affect the evasion down effect.
Both effects land: The monster is affected by Gravity.
Movement Speed Down lands: The monster is affected by Movement Speed Down.
Evasion Down lands: The monster is affected by Evasion Down.
Neither lands: The monster resists Gravity.

That allows Gravity to affect NMs that aren't immune to wind-based enfeebles.

Silence should get a similar treatment. No outright immunity, but an increase in casting time. It can still be resisted outright (say, by wind elementals), just not because the NM must be protected against those bullying RDMs!