I think that fits with Colonel Fitzwilliam's opinion that Darcy (sometimes) won't go to the trouble of using skills he actually has.

At other times, he is too distracted by his struggle against his feelings for Lizzy to show the skill he has.

We do see examples, though, of his abilities in his repartee with Lizzy. Also, in a critical situation, when he believes his future happiness is in the line, he is able to impress two strangers with his civility toward them in his ability to converse, which I think argues for a high level of ability.