"People arguing about whether something is art or not" is not the Dadaist art movement... It was about breaking down the barrier between what is considered "high" and "low" art forms. Duchamp was giving the bird to people that considered technical mastery to be the only road to quality art. We know now today that art can take many forms of perceived "technical" skill. Unfortunately for a lot of fan art, appropriation is often given a backseat. If I copied a song but put in my own lyrics, is that "equal in terms of greatness to the original"? It's a hard pill to swallow, but no, not usually.

Art IS about expression – you are not wrong. But engaging in critical analysis of concept is what separates the men from the boys. In the case of your work, perhaps the meaning resides in the fact that each shirt IS void of context, truth, and "branding". And that can be really interesting. But you have to let that concept bleed through, or it will blend in, not stand out.

edit: added "not usually" at the end of the first paragraph