I agree that Mr Bennet's words are not to be taken as ultimate truth. After all, we know his propensity to be harsh on people for the sake of witty word.

About Mr Collins, his sentiment at the ball is very ugly just like that during his first proposal. But yet we know that he's unable to carry his point. He was neither able to scare Elizabeth to accept him nor keep her to himself at the ball (though he managed to spoil her evening she contrived to partly aviod him with the help of Charlotte and, I suppose, her own). So he seem to fall short of being "powerful menace". He posesses inclination but not capability for it :)