I hate using this term, because it’s so misused by people on the internet, but it comes down to bioavailability.
At par value, most supplements cannot accurately replace the types of nutrients that you get from real food and much of this has to do with absorption pathways. It’s very complicated and not super well understood even at a research level, and I can’t even remotely do it justice here. But here is an example:
Why do we put salad dressing on greens? Is it because it tastes better? Well yes, but also because the composition of most oil/vinegar salad dressings help breakdown the cellular structure of fibrous plants and act as a transport to help your body to digest and absorb the nutrients. As a culture, we figured this out by trial and error.
If you look at regional cuisine, most of it evolved to cook and season food to optimally extract nutrients way before we understood all of this. This is why I have a lot of issues with people insisting on a particular “type” of diet being what our body is designed for when as a species we’ve gotten really good at figuring out what and how to eat to maximize energy and nutrient absorption.
So to tie this back, most of the vitamins you’d be eating with the junk food wouldn’t be absorbed, which is why a “healthier” diet would probably win out.