As far as I know, it's not entirely about some purism ideal they have in mind - the difference between the two nvidia camps on Linux is the functionality you gain with both drivers, and the proprietary driver is simply more restrictive, so, yeah, I agree that they have a point.
This is the reason I know very well that my next GPU is going to be an AMD one (given that their hardware has proper open source source by that time, that is). I bought by GPU back in 2017 or 2018, I think, a couple of years before using Linux and even considering it - had I known that today's me was going to run LInux, I would've gone for an AMD GPU right away.
Even skipping the Nvidia driver debates, the AMD hardware has been a much more consistent and pleasant experience for me on Linux overall across several AMD-based laptops that I have installed Linux on. While I did manage to get things going on my desktop that has an Nvidia GPU, it definitely caused me more headache than I expected.
I've been running this for several years now across multiple PCs, all with different hardware, including Nvidia and AMD for graphics, and Intel and AMD for CPU - and it's been working really well for me right up until recently.
After this paragraph, I will talk about the issues I've exeprienced as a gamer using my particular config. Please note that it's just a couple of minor issues, and the rest of the experience has been more than wonderful, convenient, functional, and beloved, and I do recommed Arch as a gaming setup as someone who's been running it to play games for several years in a row.
The most recent Steam Next Fest (June 2023) has revealed several demos that behaved like they launched, i.e. Steam changed my status to "in-game", changed the Start button in library, updated the playtime properly, etc., yet the game did not, in fact launch at all. I managed to play the affected demos when I switched to the KDE Plasma desktop environment on the same PC... and back on the same config after that as well.
I would consider that a one-time error that was gone by, essentially, reloading the X server, but there's been another consistent issue that I have only managed to observe in this i3+picom config. Ever since Steam's most recent UI beta, the floating elements, such as the buttons that let you install the game's demo, wishlist it, or navigate the store by the tags applied to the same game, all of which appear when you're hovering your mouse pointer over the game's thumbnail in Steam, are basically ignored; when clicking any of them, the click registers on the element that is supposed to be underneath the element you're actually trying to click: for example, if you're hovering your mouse pointer over a game and want to click the green wide "Install Demo" button, which is floating over another game's thumbnail, you'll click that thumbnail instead and open its Steam page. This particular issue persists between full PC reboots, X server restarts, i3/picom restarts, etc., and never occured in XFCE or KDE Plasma.
As I haven't been using any of the store features in Steam prior to the June's Steam Next Fest, I failed to notice any of the above, but now, I can't deny that it's been annoying. I really like my current configuration for everything I'm doing at my PCs: it's great for my work, it's even great for my gaming, it's great for my leasure, and I don't want to ditch it, because I have already tried many other tiling window managers, and i3-gaps is the one that stuck with me the most.
Now, I know there's sway, which is supposed to be a drop-in alternative, i.e. I can use my i3 config with it no problem, but sway uses the Wayland compositor, so I can't run it as easily: I'll have to set up the SDDM display manager instead of the dead-simple lightdm in order to keep the convenient multi-user setup I have, and probably sacrifice some of the performance my GTX 1080 has been giving with the proprietary drivers (I know, disgusting, but it has worked the best for my hardware as compared to the nouveau, unfortunately). I guess it's just time for me to tinker again.