Continuum, not duality
Did the person you were talking with say poly is superior for everyone? I ask because it is possible that they were talking about how it is superior for them personally and did not make that clear. That 'superior for me but not extending that to all of humanity' is often unspoken and implied and can be hard to pick up for the more direct communication inclined.
But if he just straight up said that everyone should be poly because it is superior - well he is categorically wrong. As others have said there is no 'one size fits all' relationship structure.
If your way of being in relationships makes you happy, does not hurt you or others, and makes your partner content as well, that is how you determine if your relationship style suits you.
You are not broken. Not at all. You merely have some new information to process and think about.
I have some suggestions about fitting this new information into your mental structures. Feel free to use if helpful and ignore if not.
Some of the folks I know who are somewhere on the autism spectrum tend to emphasize duality - things are THIS or they are NOT. (Lots of neurotypical people do this too.) There is sometimes difficulty in getting that some things are more of continuum - things are more like THIS and less like THAT. Thinking more in dualities will get your brain wrapped around the axle when contemplating things like polyamory, monogamy and relationships in general.
To use some science analogies, dualities are digital - they are ON or they are OFF. Ones and zeros. Continuums are more like the structure of light - they are both waves and particles at the same time - they act like waves OR particles depending on the situation to the outside observer but remain fundamentally both waves and particles.
So back to relationship styles. It may seem like polyamory and monogamy are dualities - polar opposites. And they are different, there is no doubt about that. It might seem that you have to pick one. But that is not accurate. Many people, like myself, move back and forth between monogamy and polyamory. I was monogamous - and I was good at being monogamous and it worked for me. My situation changed and now I find being polyamorous works best for me right now. And if you think about it, monogamy and polyamory are continuums themselves. For example, many people agree that monogamy is one partner, in love, sexually faithful to that partner for life or however long the relationship lasts, often with a legal basis (marriage). But not all monogamous people get legally married. Many never marry - or they get divorced and remarry. Sometimes several times! Some monogamous people consider themselves monogamous even if they or their partner is strongly emotionally attached to someone outside of the relationship but there is no sexual activity. Others consider themsevles monogamous if they or their partner has sex without emotional involvement outside of the relationship. One can argue that this is not monogamy but the people in those relationships have decided that for them, it is.
tl:dr. Relationships are more like a continuum than a duality. There is no one right way for everyone.