I would say that "se lever du pied gauche" is stronger because it's means you are in bad mood. "ne pas être dans son assiette" doesn't really mean you are in bad mood, but simply you don't feel well, or not normal.

Ne pas etre dans son assiette = Sick or ill Se lever du pied gauche = Bad day or Hangry with other people

(1) "Je ne suiS pas dans mon assietTe." (2) "Je me SUIS levé(e) du pied gauche." 1- You are sick, ill, tired, not good with your health 2- You are bored, angry, you were pissed of... None of them is more stronger, they express different statu