Yeah, the Pygmalion effect can have a positive influence too. It's just a system that say, your behavior is influenced by how others see you and the behavior of others is influenced by how you see them.
Ruby is prisoner of the Pygmalion effect as much as Loyd is. It's just that in her case, the result isn't a low self-esteem, but an ego-boost that made her blind to everything else other than her own alchemy.
She doesn't care about her flaws because she never needed to care until now. Because everyone validate that her way was good, because she showed results.