I think you are making a blanket statement about uniform systems and attributing all the bad things from a few to all of them. Uniform systems come in many varieties including gendered/ungendered, seasonal, school supplied/outsourced/local distributors, half uniforms (assigned shirt with unassigned but color coded pants), optional outerwear, regulations on haircut/makeup/accessories, and more.
Bullying absolutely happens to people who are not as well dressed, particularly people who have to wear the same days several days in a row in the absence of a uniform code. It may not have happened to you, but that doesn’t mean it hasn’t for others. I would know because I spent a good 5 years living on just two suitcases drifting from home to home, and my limited and undersized wardrobe was often a point of ridicule.
Saying “there will always be something to bully” as a counterpoint to how bullies will always find something to bully is pretty dismissive to how much it hurts to be bullied for one’s appearances. If you think that what you wear makes no difference to bullies, try wearing a clownsuit to school everyday. It’s like you’re saying “bullies will bully you anyway, so why not give them one more thing to bully you about?”
I get that being bullied for your clothes may not look a big deal to you because you’re a grown adult. But that’s not how many teenage minds work. Small things like that can be detrimental to their self esteem.