i honestly believe that the majority of "good" poly is embracing the fact that your partner has other partners. Actively accepting that and still feeling valued by them.
Some people cannot do that at all, others can do it if there is an emotional attachment but not a sexual one, or vice versa, I don't think that is polyamory, if a person needs to limit outside relationships to feel that they are "in" the "main" one. It can, however, be another relationship style under the ethical non monogamy umbrella. There is nothing wrong or lesser about choosing that type of relationship, as long as you make it clear to everyone involved what the limitations are and the consequences for breaking those boundaries.