A useless gesture is not necessarily a mistakeif it gains its purpose. In this case, Jefferson Davis, had no real expectations of peace, but, he accepted making the gesture in order to discredit and silence their opposition of his V.P. Alexander Stepens and other southern opponents to his administration.
To the extent that it silenced Stephens the gesture was more or less successful, but, as noted by others, it made little differnce in the Grand scheme of the war itself.