He is a relatively "new" Linux and has had some of the problems faced by many new users. Hell I didn't know how to install new programs that were not in the repository until years after I started using Linux. Much of the issue there is knowledge of not only the operating system but the packages included. More than half the people I've turned on to Linux went back to Windows for one reason or another, it's to be expected. You're just being defensive now.
Not really, I have seen this (guy?) do this before. Couldn't do this...couldn't do that...everything at every turn was impossible...I don't buy it.
Most people I turned on to Linux, I installed their system and setup the codecs etc (which is all done for you also when buying a WinPC) liked it a lot, probably half like you went back, and half of them did so because they bought a new computer. Others because they couldn't download Casino games or some other game they want to play. But I have never heard anyone ever say they went back to Windows because they don't like Linux. But because it can't play an app they want to.
I have had issues with Mint networking on multiple occasions. The issue was networking between Windows PCs and Linux PCs. Figuring out how to get it working properly was something that I am confident many PC users would not have been willing or able to deal with. I've had the same sorts of issues trying to get games to play on Linux. In the past week I've found videos that would not play on VLC on Linux, but played fine on VLC on Windows.
Linux does not have the support Windows does, it is not a type of OS most people are used to, so it is not as easy to use for most beginners.
True however most users don't even know what networking computers means let alone how to do it. I've had the opposite media playback issue just last week where a movie video would not work on Windows no matter which player I used but played flawlessly on VLC on the Mint machine.

As for games most users aren't gamers per se, they play what's available on the computer but don't go out and buy high end games, that's reserved for about a third of all users to one degree or another.
I would guess that for most people, a Linux distro like Mint would be as good as, or even better than, Windows 90% of the time. It's that other 10% that would keep people from wanting to switch.
A lot of people wouldn't have the first idea what to do with a Windows problem, which often has a larger, more well-established support system behind it. Asking a casual user to figure out how to fix a Linux issue, which might involve multiple sources giving different advice involving command line input, or dealing with a file system set up differently than they are used to, is more than I think most people are willing to do in their PC.
If Linux got more support from software companies, or if the various OSs had a more structured support system, more people might be willing to try.
I don't know what the issue has been with videos not playing in VLC on Linux. I can only assume some sort of codex that I have on the Windows machine/boot is not on the Linux.
I don't think Linux makes for a lesser OS, I just think Windows has such a massive amount of resources and is so widely used that it has inherent advantages that are hard for Linux to overcome. Even the fact that Linux distros are free may be a disadvantage; people probably don't trust a free OS, assuming it can't be as good and easy to use because it doesn't have the money behind it.
I'd be thrilled for companies to support Linux more. It's just a difficult market to break into IMO.