Clearly that person has never managed a 10,000 pc domain. Or hell, even a 10 pc domain in an SMB.
“The license is worth the cost” - I literally had this conversation with a peer not two hours ago. They have a client who’s previous IT management built a domain using Linux. Yes, you can do it, but I’d only do it if your IT is fully in-house and stable. This was an IT vendor. It saved them (the client) licensing…like $250 or so.
Imagine how quickly they’re going to burn $250 for a support issue because there’s something odd about how the Linux software isn’t exactly duplicating a windows DC? Or the next IT vendor doesn’t know what you implemented, so have to find out about which packages you used and how they work.
You don’t use Linux desktop in a business to save licensing costs, unless you know the use-case inside and out. The first time your business has a need for something that doesn’t exist in Linux land, all those savings are gone as you build a virtual host for Windows, and deal with the lost productivity.
And I use Linux every day for things like Proxmox, UnRAID, TrueNAS, etc. Even there the difference between design approaches is really problematic.