It sounds like you've had a rough ride and for that you have my empathy. But I disagree that monogamy would have prevented all, or any, or the problems you've encountered.
The strongest evidence against your claim is all the poly folk you dated who became primaries with others. Yes, for you it's sad that you were not chosen as the primary. But each and every one of them represents a counterexample to the claim that polyamory makes you lonely when you're old.
From your nickname to your tone to your focus on the negative aspects, your pessimism rings out loudly. It's easy to pick out one particular aspect of your life and blame that for the reason you're not happy. But that's avoidance. The reality is, pessimists don't make the best life partners.
Happiness begets happiness. Sadness begets sadness. The fastest way to find love is to love yourself. It's cliche for a reason.
I do however, fully agree with #6: hunting for partners makes you blind to what's right in front of you. Any time in my life that I've been actively looking for love, all I found was duds. Maybe we'd have fun for a bit, but nothing substantial. Eventually, I swore off dating entirely and decided to focus on having a happy and positive life with my friends and family. Within a couple months, true love fell into my lap. Blindsided is more like it.
Had you been mono and single at Burning Man, you would have wasted it just the same. Sure, because you're poly, you can spend Burning Man trying to get laid. But "can" is not "must." You could just as easily have vowed celibacy for the week and spent your time becoming enlightened. You make your own choices.
The biggest problem I see with your attitude towards dating is the very notion of seeking. When a person searches for romance to fill the void and make them happy, that emptiness glows like a lighthouse that beams "Stay away!" People are naturally drawn to those who are happy, healthy, and whole. Focus on those three aspects of yourself, and then romance becomes irrelevant. Coincidentally, focus on those for their own sake, and love tends to find you without any effort wasted on searching.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker