When Fred Wilton came up with 'The HNV Theory' back in the 1970's I don't think that he was wrong, but I do think that it has been unintentionally misused, misquoted and misinformed.
I think from memory he reckoned that after watching rabbits in Australia chew wooden posts to get an additional mineral that was missing from their food, carp would search out foods that provided all the nutrients they required. His answer was to come up with a milk protein boilie or paste providing everything nutritionally they needed. Skinning the paste made it small fish proof. This is where it gets difficult; milk protein is not the easiest protein to digest requiring a specific enzyme, lactase.
If there is no or limited amount of lactase, the milk boilie can't be digested, filling the carp up until it is excreted. This brings up that milk protein baits don't need massive amounts of freebies.
Milk protein baits were effective, especially so when an additive called Bengers was added. Bengers contained amylase, trypsin and lactase, helping with the digestion of the baits. The Bengers meant that larger quantities could be used.
Then we have the 'revolution', from a guy named Hutchy...
He disagreed with Fred Wilton, not over the theory, but on the best source of protein; he believed that the best protein source was fishmeal.
We move on in time, where the only non meat best protein source with easily digestible and fully utilisable proteins is yeast. Now I'm sure Mainline have got that down to a T, their baits may not be high protein, but everything is useable, from the roughage, the protein and carbohydrates.