The correct way to test that a specific value isn't contained within an Array is...
<<set $list to ["one", "two"]>>
<<if not $list.includes("three")>>There is no "three" in the array.<</if>>
The <<switch>> macro is designed to determine if the single value passed as an argument to it is equal to one of a set of specific values. (the values passed to each of the related <<case>> macros)