As
Xul said, you seem to be confusing what Kettle Sour means. It is a process rather than ingredients, and that is a pretty set term. I wouldn't say it is a "bad word", but it is associated with a product that has a higher probability of not being as good (obviously subjective) as other methods. Same with using extracts instead of "real" ingredients.
There are plenty of traditional berliners (and gose, and other sours) that are just sach and lacto but are not kettle sours.
There are a bunch of terms that are up for debate "sour" beer groups, and a lot of breweries that do not hold to these at all (breweries calling kettle sours "wild", the use of the term spontaneous when cultures are pitched, etc). Though, kettle sour is not one of those terms. It would be like arguing the term "mash" or "sparge".
To me, I define things as such:
Kettle Sour: Quick lacto souring, followed by boil of wort and addition of sach
Sour beer/ale: A beer made with lab controlled cultures of lacto/bacteria/brett
Wild: A beer made with naturally captured lacto/bacteria/brett, whether through a starter placed in the open or cultivating off of something (fruit, bark, etc)
Spontaneous: A full batch placed in an open environment where no culture or yeast is added, only natural yeast/bacteria/brett in the air cause fermentation
The couple things I am not sure where to place are;
Brewing a beer from dregs/cultures of other beers. Obviously some of these are just stepping up lab made yeast. But what about stepping up things like Cantillon and 3F? Typically I file this under "Wild", unless I know the source is 100% lab made, the it would just be a sour.
Using only natural yeast/bacteria/brett off of ingredient without stepping up or cultivating these microbes at all, i.e. adding fresh stone fruit to a full batch of unfermented wort and letting nature take its course. I can see this being described as spontaneous or wild. I have called a beer I did like this spontaneous, but I think I have shifted to feeling this is more "wild", as there are other microbes in an environment that won't come through on the fruit.
Obviously this is dissecting terms more than it needs to be. But I feel the first (kettle sour) and last (spontaneous) terms should be well defined terms. The first because a lot of times this is a simple and near "cheat" version of a "sour" and the customer should know that is what it is. I want to know if I am getting something like Fruitlands or Palace of Cracked Heads. Spontaneous is a significant term to me because it indicates a dedication and risk to delivering a specifically unique beer. Using the term spontaneous when there was nothing spontaneous about the process is trying to claim achievement and credit for something undeserved.
Most of this is just my meaningless and worthless opinion.
TLDR: I just felt like going on a little tangent.