A delicate meaning difference.

I'd like to ask the meaning of the following sentence:

"He’s old and not really all that good on the whole, but he can nail lefties without being out of his depth against same-handed pitching."

I almost certainly believe it means that he's good at dealing with lefties as opposed to his ability to deal with righties because of the word AGAINST. (In other words, I thought the writer was trying to say he's much better dealing with lefties than righties.)

My question is, however, someone strongly advised me that the meaning of sentence has NO underlying implication of comparison. and, I should read it like "he's not bad playing against righties but also good at playing against lefties"

In summary, I was originally thinking that the player was good against lefties, but bad against righties.

He's thinking that the player was good against lefties, and okay(or not bad) against righties.

Can someone clarify this? Which opinion is more acceptable in this case?