While I agree that Mr. Collins' stupidity and tactlessness is more showcased in this letter than any cruelty, and that Charlotte's marriage will be often uncomfortable, I hope that further exposure to Charlotte will (in time!) teach Mr. Collins how to better phrase his less admirable sentiments.

However Charlotte disapproves of Lydia's behavior, her first impulse, I am sure, will be one of sincere concern for Elizabeth and the family.

This is another example why Elizabeth was right to refuse Mr. Collins, to my mind: had Mr. Collins written a letter like that to someone she liked about THEIR relation's problems, can you imagine how mortified Elizabeth would have been as his wife? She would probably have told Mr. Collins off in no uncertain terms! Had she been there when Mr. Collins was tattling to Lady Catherine, how could she have kept quiet? I am sure that Charlotte, disliking it as much as Elizabeth, would still be able to control herself enough to keep what influence she has, thereby being more able to stop any future improprieties...