Protein help with satiety? Yeah maybe it does, but fat, and in particular saturated fat, helps even more. And carbs hold more water than the other macros. But none of that matters because a calorie is still a calorie
So what if fats help with satiety, calories in vs. calories out equals gain, loss, or maintaince of bodyweight. But of course you must also take into account activitiy level and metabolism. I guaran-goddamn-tee you if someone who supposedly can't gain weight, just sat around on their ass all day and ate a legit 5000 cals a day, they would gain weight, no doubt about it. And if weight loss is the goal, eat much less calories than usual, but I you can't handle and deal with the hunger, then just take some crystal meth, coz that will take care of your hunger pangs :>