I agree with you that Mr. Bennet's response is not so over-the-top. Mr. Bennet has only heard decent reports of all the officers in stationed in Merryton, who will now be in Brighton. He didn't hear of any men preying on young women (such as Darcy's account of Wickham with his sister), of whatever level of wealth. And he considers Colonel Forster to be a sensible man, who will keep his own wife and his wife's friend out of any real mischief. Mr. Bennet did not read the reprimand Mr. Darcy wrote about his observations of the Bennet daughters, which I would imagine would have put Mr. B on the defensive had he read the observations. Mr. Bennet is also used to dealing with silly daughters, so he's reverting to the idea that Lizzy's falling prey to the same worries as her sisters. Mr. B is no more guilty at this point in time than someone like, say, Sir William Lucas, if Maria were given the same opportunity.