The people of Egypt were having regular problems with drought, loss of food production, diseases, deaths, etc. If someone had a 'dream' it was only on the bases of his brain mulling over these problems as this is what the brain does in sleep; dreams are based on our lives that we have already had.
A Messenger is given the social and political means to solve our problems, our SALAT, and one aspect of this is doing things knowing that they have a result in the future, cause and effect. So, wahi or common sense said that if there is drought, then save for the 'no rainy day'!
Every good person has the right to hold to account their leaders and there is no such thing as blind, unquestioning obedience to anyone as 'God's shadow on earth'.
If they are doing the right thing, promoting social justice, harmony in society, human rights etc then we must help and work with them towards achieving this.
Those who are hell bent on promoting themselves, working against others, opposed to peace etc are the ones condemned in the Quran as they have no interest in the common good, these should be stopped by whatever means are required.