That’s not what he means. If he was born with that hearing loss, it’s unlikely that there are brain areas available at the high frequencies that he is missing for the CI to take advantage of. The brain doesn’t like waste and will take over unused areas for some other function. CI outcomes for pre-lingually deaf individuals are very different and there isn’t a huge population on this forum to talk about their results. You cannot really generalize from the experience of post-lignually deafened individuals.
In your position, I would probably go through the candidacy process and seriously consider an implant for the left ear. Particularly given the growing number of cases I’ve been seeing where residual hearing was almost entirely retained after implantation. You’d want a stellar surgeon.