One thing this thread has opened my eyes to though is that I was definitely naive in thinking all children in a family would/should be treated equally and that step parents would love step children as their own
I think it's probably a common misconception when you've not experienced it first hand.
There are situations where fair treatment is right and situations where completely equal treatment is wrong. You have to make a judgement. For example with wills, it's not fair imo that any inheritance from me should be split between my child and my SC as they have two parents to inherit from themselves. However, day to day treatment in the home when we are all together is fair.
The loving as your own is definitely a misconception in most cases I believe. I think most people who've never been a step parent don't appreciate what a big ask that is of another person. I could never love my husband's child like my own, if circumstances were different perhaps, but not in our set up.
People will falsely compare it to adoption and say 'you don't have to be biologically related' but it's not about that to me. My step children have a mother, I have never been needed in that way by them and as such, that maternal bond and instinct is not there in the same way it would be with an adopted child. An adopted child is still your child who you have parental responsibility for. Step children are not, especially when they have two involved parents.
It is not the same as your own children the majority of the time imo. And I think most step parents don't love them like their own if they were being honest (again, certain circumstances aside).