Just wanted to say, while no I don't think partners need to basically 'dump' or push aside other relationships to work on the one in trouble, I dont' see anything wrong with taking more time with the relationship that needs a little help. Not as a way to shore things up but to actually work on things.
For example, if hubby and I are feeling disconnected, or having issues with things that have happened in the relationship in the past and how we dealt with it, then we deal with it. We decide to do things together to reconnect. We schedule a movie night, we sit and talk about things to work out. We read a book together, even took quizzes together on finding out our love language, or apology language. Things to help OUR relationship. I didn't need to pull back from my boyfriend to do that, simply tell him, "Oh yeah hubby and I have a date night this Wed."
It's a difference in telling boyfriend that I need to take space from him so I can work on problems with hubby, (which honestly isn't anyone's BIZNAZZZ but ours), and taking the time to schedule what time and things I need for each relationship.
So maybe it's your wording. You want to take time to work on a relationship that could be having trouble? Okay do that. You want to penalize other relationships for it? Um, why? That's like punishing the cat for the dog getting into the garbage! (bad example but I cringe at the multi kid ones used for poly.)
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year