Linux definitely replaced Unix servers. I remember calling Digital Equipment Corporation rep in the UK in 1994 for a quote for a server and was told I'd need to pay a minimum of 100,000 GBP for a minimum running config. That's 200,000+ GBP in today's money for something that had less power and storage than a RaspberryPi with an 32GB SD card. Yes, the price included the license for the operating system and the http server.