"Competitive residencies" can mean different things
In the inherently competitive specialties, in which every program is competitive e.g. the surgical subspecialties, sub-i performance is more important. This is mostly because they are small fields and the importance of any one individual to the whole program is high. We want to judge whether you will be a good fit, evaluate your work ethic, etc. And although it probably says something about your academic ability overall, my field is so different from medicine and psychiatry that I don't really care at all how you did in them as long as you passed them like a normal human being. In fact if your psychiatry attending was so impressed that you spent two hours a day on your rotation debriefing on transference and countertransference I'd wonder if you're a good fit for us (not saying you should strive for anything but the best grades).
Almost every field still has competitive programs irrespective of the overall competitiveness of the specialty. In those cases your overall grades probably matter much more, first of all because they are more likely to be the ones that are represented in core rotations in the first place. And then some such specialties don't even really have dedicated sub-i rotations, at least not like the ones we offer.