Quality of partners is less an issue of poly versus mono, and more an issue of individual personalities.
In a monogamous relationship, a partner can be unsupportive and unable to deal with your crises. They might choose to stay longer hours at work, hang out with friends, or just go to sleep.
That's not to say polyamorous partners are some kind of superheros that magically know exactly what you need and come to your rescue and solve all your problems. We're just as screwed up as the rest of the world
But being poly does not make us inherently more so.
I try to be careful about things like "asking for anything you want in a relationship." It sets up unrealistic expectations of perfection. No relationship is perfect and there will always be compromises. It's important to have boundaries and needs, of course, but to me the wording "ask for anything" implies putting requirements and limitations on your partners that may be unrealistic.