Mac OS X Server isn't what it used to be
As your colleague pointed out - https://www.theregister.co.uk/2018/01/29/farewell_to_macos_server/ - a few months ago, Mac OS X Server has been thoroughly gutted. Gone are the mail server, web server, VPN, and more. It's now just a tool for administering other Mac and iOS devices.
Of course you can still use a Mac Mini as a departmental server; but you'll need third party tools, and you can no longer expect Apple to support your efforts.
Biting the hand that feeds IT
