There's many factors that contribute to the price of dairy product. Dairy is used for a wide wide variety of things. I don't think that subsidies are a relevant factor in the case of the waste products. If dairy wasn't subsidized, dairy wouldn't stop being used and those waste products would still be created and we are back to where we already are. If those waste products are still going to be produced, there may be less of it but still far more than needed and so there is still excess

I'm not overlooking subsidies, but I don't see that is relevant. Since the subsidies are not in anyway for the production of dairy by products.

As an example where I am they are subsidized to create a system that will never run out of dairy as a consequence of WW2 era rationing my country decided we will never have a dairy shortage again. It was and still is(or just had never been reassessed) deemed too important to have milk and all the things they can do with it and how powerful it is as a source of nutrition in tones if scarcity because it ticks a lot of boxes.

Also the alternatives are also subsidized so I don't see it being a useful point to consider.

So if you are calculating the cost of this by product to costs it's cost effectiveness against the alternatives you also then have to calculate those subsidies for the alternative options as well. And if we eliminate subsidies from both sides of the comparisons then those other options sky rocket and only makes these by products relatively cheaper to use. Being that the alternatives subsidies are for the alternatives themselves. The key thing here is that it's a by product of another product(s) and will always be available in quantities that are unable to be fully utilized anyways

They just won't stop making dairy products even without subsidies. And if they stopped subsidizing it there would be a significant reduction in the amount produced, but as I understand the industry that won't make a dent in the amount of these by-products needed given how little of it is actually used compared to how much is produced. I might be wrong on that but it is how I understand things to be and is what's informing my opinions here.