I’ve never seen mainstream feminist voices say women are superior to men.

I haven't heard "women are superior to men" either.

I have heard (from women and men...some who say that the are feminist some who don't):

1. Women are better communicators

2. Women are less violent

3. Women have higher emotional intelligence.

4. Women are more thoughtful

5. Women are more moral/ethical

6. Women are more compassionate

7. Women make better leaders

I have heard (from both men and women...none who are feminist):

1. Men are more logical

2. Men are less emotional

3. Men handle stress better

4. Men have more confidence

5. Men make better leaders

I think it's possible for men and women, including feminists and non-feminists, are human and are subject to the same biases that anyone else has.