My ex had a child when I met him, and that was the most 50/50 care I've ever seen before or since. I can't say I agree with how his care was handled, as it was very much whoever was available in the family would have him.
By the time I left, I had him the most. I did his parents evenings, dental appointments etc etc. I remember missing my friends birthdays cause I was de facto sitter.
That wasn't okay.
I think it does differ between who has primary residency. So my daughter's dad is her step dad, but been around since she was barely a year old, he has PR, etc etc so yes he's an equal parent and he behaves as such.
If we were to divorce, and him get a new partner, I'd expect her to treat our children with care and respect, and hopefully as time moved on, with love. Not unlike a good aunty.
I'd expect that is what would happen, because I know my husband and he would only be with a woman who could do that.
In return, I'd respect her position as his partner, and a figure in my daughter's life.
As I had quite a tumultuous childhood and teen years, I fully buy into "the more to love, the better" because often, children need a safe adult that loves them to talk to, before they dare speak to their parents. And I will foster that in my children and other adults around them, in the same way I want to have that relationship with my friends children.
Does that make sense?