[Dr. Sivana]

but since WHEN has - been used instead of:, ; (), etc.?

My Warriner's taught me that a dash ("--" on an old typewriter, NOT a hyphen) was used when a contrast or comparison was being made. It is a thing, and widely used in newspapers even in the 1970s, but more commonly used since everyone has access to real typographical characters.

The semi-colon has all but disappeared, and it is very rare that business correspondence begins with a proper colon, rather than the informal comma ("Dear Mr. Smith:" rather than "Dear Mr. Smith,").

[nopardons]

I haven't had cause to write a business letter in an extremely long time, NEVER used the - and neither did my secretary.

I still use ";" when I write and do so correctly!