If you have several kernels you might want to disable the fallback kernels. You do so in the .preset files in /etc/mkinitcpio.d/
But yeah this is the downside of using flatpaks. That’s why I think it’s better to avoid flatpaks and other similar sandbox environments. I know the Linux community are desperate for the increased stability and supposed benefits to security but you’re paying the price in worse performance and high disk usage.
Yes I think you’re right, there’s probably a significant overlap in the target audience of GOG and Linux users. I guess the reason why GOG hasn’t released a Linux version of GOG Galaxy might be because a large portion of their catalogue is Windows and doesn’t want to include something like Proton or Wine support. I don’t think it absolves them from criticism however.