I don't consider size to be the primary determiner of how banks operate re: good or bad. I consider the ownership model to primarily determine incentives and behavior. They are, of course, are not uncorrelated, but rather when attributing primary cause, I see credit unions incentives aligned with their clientele because they are one and the same. Whereas banks have a larger discrepancy between owners and customers.

A bank exists to serve the interests of their shareholders, a credit union exists to serve the interests of their members. Unless you happen to be a significant shareholder in your bank, credit unions are more aligned with your interests.

All things exist to serve the interests of itself.