While parrots may have an independent streak as well as not responding well to orders, they are not really dominant in nature. Many of them prefer to perch is high places, but this is because they live high in the treetops ( canopy dwellers), where they are much safer from predators and not out of dominance. Greys, are no exception to this even though they are partial ground feeders. Any actual dominate type behaviors in parrots, it there are any must have been taught to them by humans as this trait does not appear to exist in wild parrots. Perhaps you are misreading your parrot.
Mash is nothing more than raw fruits and vegetables that have been run through a food processer or blender until they are of a consistency similar to that of oatmeal. This is often done to keep the bird from picking out its favorite foods from the mix, when the same ingredient are simply cut into pieces and served to the bird it is referred to as chop. I would not and any new pelleted foods to Alex's diet, but I would try making a mash and using one of the commercial foods that you are already giving him as sort of a top dressing for the mash until he begins to eat the mash. I feed my Grey for breakfast and for all day feasting Gloop and a fresh raw fruit, a fresh raw vegetable and a fresh raw leafy green with the fresh raw foods changing each day. I also feed my Grey a no sunflower seed mix with the addition of two or three tree nuts for her dinner. Gloop is a home made cooked food that is roughly 40% partly cooked whole grains, 40% mixed vegetables and 20% fully cooked navy beans and lentils.
What is Alex doing that makes you think and feel as if he is behaving in a dominant manner?