"It appeared that the use of colon-operator ... is incredibly slow or inefficient"
Unfortunately those timings are meaningless as they compare apples with oranges.
"Why is the use of ":" / Colons 70 times (!!) slower"
Slower than what: not doing that operation? Not doing an operation takes zero seconds, so the factor is infinity.
Note that you are comparing two totally different sequences of operations:
- allocation of a variable to a new variable, which uses no new memory (just adds a pointer to the same array).
- subscript indexing into a variable creating a new array in memory to be allocated for the extracted elements (all 125 million of them), and then allocation of that array to a new variable.
So really all you are measuring is the time required to create a 125 million element array.