Sometimes the designations are descriptions of the relationship model.. describing time invested, or the time allowance. It can mean other things too.
I know I don't use it as a descriptor of how much I love someone.
I don't believe I could time manage two primaries. I have a wife, we want kids, we have 11 years invested and a lot of things in our lives both planned and in the past.
If I had found someone at the same time as my wife, sure, maybe. Different time and place. But as it stands right now, I can't foresee having two primaries.. or having "all things created equal"..
I know I can love equally, I am doing it and have done it..
.. those designations will never describe the level of love I feel for someone.