Even with natural food, the sources that have enough protein do not have enough vitamins (even with egg yolks, which contain more vitamins than almost any other

Even with natural food, the sources that have enough protein do not have enough vitamins (even with egg yolks, which contain more vitamins than almost any other protein-rich food, you cannot eat enough egg yolks per day to cover the required daily intake for all vitamins), so you must combine a variety of foods. If you have a source of pure protein, like this fungal ovalbumin, you have a much greater freedom of choice for the rest of your food, becoming able to select other items only for their vitamin content, without caring that they may contain too little of the major nutrients. Therefore, with such artificial complete proteins it would be easier to eat enough vitamins, not more difficult. As a general rule, it is much easier to compose a diet from various food items, each of which is rich in a single nutrient, than to compose a diet from food items that contain a great variety of nutrients, but a few of the nutrients are missing in each food item, so you must make a complex balance of the quantities in order to have neither too little nor too much of each nutrient.