Nobody is naturally good at relationships. And anyone who thinks they are is probably making their partner miserable through being a know it all. It's a learned skill, and I think you're right in that a lot of women believe they are awesome partners when they aren't. I'm definitely not.
I also think in relationships we tend to dehumanize our partner at times. We forget that they are just like us and that we are hurting them with the words we spew. I write a lot about men's failings in relationships because they tend to be more overtly abusive and/or violent (plus it's what I have direct experience with), but the insidious nature of women's abuse towards men can be just as damaging.
I wrote an article about what the point of relationships is because I think most people believe they're supposed to find a partner that completes them, but the truth is our partner is a mirror for us - to show us what needs fixing inside ourselves - that we wouldn't be able to see without someone reflecting back to us.
It's here if you're interested: https://medium.com/long-after-the-thrill/relationships-whats-the-point-c680f6671919