Plenty of anecdata of people who stopped eating certain categories of food and certain conditions they had for a long time went away. In my son's case, a severe case of eczema that persisted for years went away in a matter of weeks after we significantly reduced the amount of hydrogenated oil products available to him to eat.
Sure enough, when we would visit my mom's place which had it, and he'd indulge, the symptoms came back. Same thing when we would buy it at home and he's splurge, he'd have the same problems recur. Cutting it out of the diet is the only thing that correlated highly with the absence of the condition. This happened even after a move from one state to another.
One case, not proof, but definitely repeatable in our circumstances. I have heard a LOT of similar stories. Is it proof? No, but it's an amazingly easy thing to try. It's takes an adjustment, but it intuitively makes sense. Processed food of today is something our ancestors wouldn't even recognize as food. It's just not what our bodies were designed to handle. Some can handle it better than others, but such a processed food and artificial sugar-heavy diet can't be called natural or even healthy.
And the meat they did eat was lean game meat. It was high in unsaturated fats - like our modern day oils. Not like a steak. A steak is a product of farming. It’s a new invention, <10,000 years. Prior, humans ate almost exclusively nuts, fruits and foliage.
Yes oils are “refined”, but humans have been eating unsaturated oils predominantly for almost all of our existence. The proliferation of animal fats is very, very new. Really, it’s past 100 years. Before that meat was rare, it was a delicacy, very expensive for people.
Now, high sugar is a different story. But the oil thing is complex, it’s not as a simple as oil bad animal fat good and natural. No, it’s very unnatural.
Meat only became more of a luxury in the agricultural age where we started squeezing more and more people into smaller and smaller regions which meant there was no longer enough to go around. So plebs got the carbs, and royalty got the protein. FWIW you can also see this in the groups that have ancient traditions dating back far into the past, like the various tribal groups in Russia, Mongolian nomads, etc. Meat, and many highly creative ways of preserving it [1], remain the majority of their diet. They probably don't date back to the paleo, but at least far back enough to falsify the claim that animal fats are even remotely novel.
[1] - https://www.rbth.com/russian-kitchen/334150-dish-kill-kopalk...
Also, simply cutting out junk food will absolutely not reverse fatty liver. You need to eat less and lose weight.