We only use whey isolate and whey concentrate for 2 reasons:
1. Protein bioavailability (BV) is the amount of protein your body can actually use when you consume it. Whey has the highest BV of any protein on the planet.
Whey has a higher BV by 20-40% when compared to egg, meat, fowl, and fish. That percentage is even higher when compared to casein and milk proteins.
This means that gram for gram, your body can use whey better than other other protein source available.
2. When companies add additional proteins to their products, they dumb down their formulas, take advantage of FDA loopholes, and create a cheap product by minimizing the expensive ingredients.
Yes, whey isolate and whey concentrate are the most expensive types of protein, even moreso when they come from grass-fed cows, but they are also the only ones that work better than food.