Does "better" include "more like the in-group"? If yes, this seems very plausible. If no, I'd guess the crony beliefs cluster is a bigger source.
Better in a locally zero-sum way has some direct checks (because the people you're interacting with you have an incentive to see if you're deceiving them about your usefulness), whereas locally positive-sum biases (e.g. "my in group is the best in-group, and is right about everything") should be selected for.