It works though. I don't think we disagree much on the principles, but the two concepts are intertwined. If you sit down and stuff your face with e.g. sausage and cheese you will still get an insulin response and you will absolutely gain weight. If you eat well beyond your daily maintenance, I don't care what you're eating, you're going to gain weight.
It's simply a lot easier to tell someone to watch their calorie count and eat good food than it is to tell them to monitor their insulin levels. They get the second bit right if they do the first.
Perhaps "spike" was a poor choice due to connotation, but proteins and, to a lesser degree, fats, do in fact provoke an insulin response (certainly less so than carbohydrates) via gluconeogenesis[1]. I'm not an expert, but my understanding is that this is why it is important to not exceed a certain % daily intake of protein when on keto and to keep fats high (aside from fats being your primary energy source.)
AFAIK, the primary issue with too much protein on keto (gluconeogenisis) isn't the change in blood glucose, but rather that GNG blocks ketosis.
That's the opposite of the diets goals, is an easy issue for people to incur while thinking they're on track, and keto can make you more susceptible to GNG :)
Sausage and cheese is totally kosher: in moderation, ideally beside some leafy greens.
It's simply a lot easier to tell someone to watch their calorie count and eat good food than it is to tell them to monitor their insulin levels. They get the second bit right if they do the first.