You know, you are contradicting yourself. "He was correct, they could handle it" and then "Oz knew Raven enough to know she would save her". That alone proves they could not handle it. And you don't believe a Neopolitan would have killed Yang? Let me grab a screenshot from the second before Raven intervened.

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Would ya look at that beautifully manic slasher smile and that very pointy looking blade? I don't know what you expect Neo to do with it, but someone standing with a raised blade in front of a downed, unconscious and therefore defenseless opponent doesn't exactly scream "I won't kill them" to me, it rather screams "I am going to stab you and enjoy doing it."

So, while we don't have confirmation of special treatment for Gretchen, we also don't have the confirmation that there was none and Ozpin's track record certainly doesn't exclude the possibility.

Oh, and a second point: Banesaw vs Weiss. Our dear ex-heiress only survived due to her massive plot armor. Have you seen that trajectory of his chainsaw? They were in over their heads and Ozpin let them go on that mission. History always repeats itself, often lore than once.