I sort of see that point, but Gunn has made some pretty bad decisions that he can't blame on the defense. You could make the opposite point that maybe the defense would do a better job if they had more confidence in the keeper. Or perhaps both the defense and Gunn would do a lot better if they weren't so often exposed and outnumbered on counter attacks by poor midfield play.
I don't think there's an easy solution, or even an easy solution-solving process here. The attack looks sharper and more organized this year (perhaps because the pressing is starting to work), though we still lacking the end product. Everything else looks like a mess. Ralph has to figure something out and he's got his work cut out for him. IMO, he can't wait for the defense to sort itself out because it could take awhile... or it may never happen. I think he has to take a hard look at Gunn's recent performance and strongly consider making a switch. If he decides to go with Gunn, I'll be okay with it but we're too deep in the season now to think that things will sort themselves out on their own or there's some simple, minor fix. He's been toying around with that backline all season to no avail.