Staying at 8-10% body fat without steroids or SARM is nearly impossible, even if you hit the 0,001% genetic lottery.
No it isn't. It's very doable for the genetic freaks that are pro athletes, it just wouldn't be optimal for performance.
Football players and athletes stay around that body fat level almost 365/365 days
No, they don't. More like 10-12%
Take the Goretzka or Bale scenarios. They gained like 8-10kg of lean muscle mass in a year.
How do you know this?
That's fecking impossible to achieve naturally even if your only goal is to build muscle and you're not doing anything else
An untrained young male can put on 10kg of muscle mass (not lean, mind) in ~ 4 months. It's what happens when you eat and add 80kg to your squat. It's sounds very easy to put on that amount of muscle if you have 8 more months and freak genetics with little prior lifting experience, now that I think about it.
(we're not talking about gaining 8-10 kg of muscle mass in a year, that can be done with bulking, we're talking about adding serious size while being at 7-8-10% body fat).
No we're not. Where's your source Goretzka and Bale were on 7% bf during their bulk?
Add tens of thousands of miles of running during a year and it's god damn impossible even if you're a Greek god. Also should be taken in consideration that football players somehow build that muscle mass during the off season, they magically gain some kgs of lean muscle in periods where they're not drug tested.
Long distance running is highly catabolic. The stress of football training inhibs adequate adaption to heavy weight training. Without grueling 2h sessions, adding some kgs becomes very easy.
Or should we believe that Cristiano is at 6% body fat as a natural for the last 8-12 years?
No, because it was reported that he was at 7% just 3 years ago. Ronnie is also the biggest genetic freak on the planet.