Each species of Parrots have different responses to Sunflower seeds.
As a general statement, too much of a good thing is bad. The problem is that far too many Humans feed near 80 to 90% Sunflower seed and that volume is too much for any species.
Look for a quality seed mix that contains a wide cross-section of seeds, grains, nuts and other items like dry frozen veggies, pasta... To this mix add pellets appropriate for the size 'or' liking of your Parrot.
Note: All seed based mixes should be frozen when you bring the package home for a minimum of two weeks and better four weeks to kill any bugs that naturally exist in such mixes.
Both peanuts and Sunflower seed should be limited in the amount provided. Your goal should be a wealth of fresh foods with the greatest mass being green veggies and then spreading into the other colors and varieties. The dry food being served as support.
I'm an Amazon Snob, so I have a limited knowledge of the best diet for your Parrot.
If he has too many it can cause him to become sick long-term. 1) It will fill him up without much nutrition (so he will eat fewer foods because of all of the sunflower seeds which are not very nutritious). 2) They can lead to liver issues etc due to high fat content.
I feed my Green cheeked conures once a week with a handful of sunflower seeds only when they are breeding, to give the chicks a little boost
An article written by a famous Australian aviculturalist by the name of Stan Sindel, he did a study with feeding on French White millet only as well with the addition of fruit and veggies, compared to feeding a mix of sunflower and other seeds. The results were astonishing and birds of the millet diet were living longer, healthier lives in collections of birds around the country- They don't call Stan Sindel the 'Father of modern Aviculture' for nothing!
Black cockatoos are an exception, with them requiring amounts of sunflower for their high fat diet, that they would normal obtain through their natural diet of pine and casuarina nuts
Thanks
Noah Till