If you are asking the question whether UPF is bad, surely you got to control for the amount. Of course you can say that people tend to eat too much of UPF simply because it is easier to prepare and eat, but that doesn't mean it's the processing that is bad for you. It's still just the amount.

So rather than apple juice, consider watermelon juice. The nutrition and fiber are unchanged, the volume is close to 1:1. But you can drink more than you can eat.

But that's part of it. There's a part to do with the nutrient quality, which can also be talked about, but also a part that has to do with how UPF are consumed. The act of processing the food a certain way makes you eat more of it without realising it. Same with fat and sugar, eating a stick of butter on its own is hard, same with pure sugar, mix them up and it's delicious and addictive which leads to health problems.