I know, I caught that. That's why I said 3000 is much more reasonable than 6000. I also just emphasized that it's unlikely that 2,600 was "way low' as you said.
Eating clean vs "dirty" won't make a major difference in fat gain when you're in major caloric surplus. Even with ideal protein intake muscle growth has rate limitations. The law of conservation of energy mandates that the rest of the calories must go somewhere since your gut is highly efficient at absorbing macronutrients and you won't simply crap it out. This means the rest will be stored, and you will get fat.
Now, the issue with getting fat isn't simply cosmetic. I see people day in and day out, big muscles and small, who have major health problems from getting fat. Almost every major morbid condition affecting Americans today is related to having too much adipose tissue. One that really hits home for a lot of people is diabetes. Adipose tissue directly causes insulin resistance. If you're a person with a predisposition to Type II diabetes, you might unmask it. And, this is a problem because of the vicious cycle that ensues. Get fat, insulin expression increases --> amyloid protein is coexpressed with insulin and deposits locally in the pancreas, destroy the already fewer beta islet cells meaning that your pancreas now has a more limited ability to respond to the hyperglycemic state. You get fatter, insulin resisntance increases, and your pancreas keeps killing itself. All the while every small blood vessel in youry body is hardening, your nerves are getting wrecked, and your body is in a pro-inflammatory state which starts negatively affecting larger blood vessels, liek those in your heart, brain, kidneys contributing to the development of organ failure.