...it is very rare for a self-aware person who is willing to personally develop and work towards goals to be unable to get a 1:1 relationship if that is their desire.

It's all about what you want. I would happily go below 1:1 (though generally things are more complicated than ratios), because the values of the factors you listed are very different for me than they seem to be for you.

• The difficulty in acquiring sexual or emotional partners: Moderate but not unduly burdensome.
• The cost of being committed to a particular deal: Low. If the relationship is a net loss I would want to leave anyway, and if it isn't then it doesn't preclude me forming new ones.
• What influence having a partner has on wellbeing: High. A shared partner is definitely better than no partner for my wellbeing, and a shared partner is even generally superior to an unshared partner, not least because of compersion.
• What level of aversion one has to handing over power for meeting a need to another individual: None. If I have a need I can't meet myself, allowing someone else to meet it is a pretty good deal, and even if they stop I'd be no worse off than before.
• What level of satisfaction of needs that a relationship is intended to fill is a 1/3 partner likely to meet: High. For the most part my relationship satisfaction doesn't totally correlate with the amount of time I can spend with a partner, and whatever time is needed to maintain the relationship properly is usually enough to be reasonably satisfying.

Preferences should always determine lifestyle. I realize that our preferences are radically different, but that doesn't mean that I and others like me are necessarily getting a "bad deal." I suspect that if I were to take your approach it would make me miserable, but that is not a criticism of your approach.