Those are equity, not currency. There is a reason why employees of those companies get paid in local currency, and not company stock.

Apples and oranges. Stocks serve a radically different role than currency. But you are very right about one thing: cryptocurrency behaves a lot like a tech stock.

When's the last time a major index lost 50% of its value? - 2008 crash due to deregulation

Does it happen every two years? - obviously not

Are stocks intended to be currency? - no

Stocks also are attached to real property - ownership in a revenue / profit generating company and their assets. Crypto is only a vehicle for speculation.

A currency should not experience regular crashes or explosions of value. Assets are generally more volatile by their very nature.