I mean it's not even my own problem. I just have Spotify, Microsoft Teams and Zoom installed that way, and a few pieces of software that I'm testing. I use a rolling distro so I have the most recent versions of every software I need anyways. And I have the skills to configure stuff. So I myself don't have an use-case for a spyware-riddled Chrome browser from Flathub or something. I have a nice LibreWolf from the unstable channel of my distro. Steam and all the other stuff is there, too. And it works almost flawlessly. Why would I trade that in for a 4GB version of the same software that has downsides?

It's the newer users I'm concerned with. Their sub-par experience of Linux.

This is what I mean:

• https://github.com/keepassxreboot/keepassxc/issues/7352 (Maybe Keepass works as of now(?) I don't think so but I haven't tried. At least some addons do. But other's don't. It requires the permissions to be configured by the prople preparing both flatpaks that want to talk to each other.)
• https://itsfoss.com/flatpak-app-apply-theme/ / https://docs.flatpak.org/en/latest/desktop-integration.html
• All the issues people had with Steam, the graphics drivers, attaching gamepads/controllers or headsets, getting Discord and extras working. (Some of that seems to have been resolved in the meantime. They put quite some work into it.)
• Some distros don't update Flatpak packages as part of their standard update mechanism. You need to learn to regularly run "flatpak update" or learn how to activate that.
• I have some packages still rely on old runtimes that are missing security patches. I suppose it's the same for a lot of other people. And there isn't a mechanism to warn you. You also need to learn how to figure that out.
• I don't remember which of the video conferencing solutions this was, but I remember fighting with the webcam permissions and advice on the internet was to disable sandboxing entirely. I set the permissions a bit better but then also screen sharing wouldn't work.

As I said, it's okay for someone like me - and probably you - to use, and I don't complain. I'm glad I have Flatpak available as a tool. But look at the issues I've linked above and the steep learning curve for the beginner. They need to learn what GTK is, what QT is, what desktop they use, learn what Flatseal is, use the CLI. They have no clue why it is even required to do that much work to get their Keepass set up. And that it's not Linux' fault but their decision from 2 weeks ago to install the browser that way. And their experience is just worse than it needs to be. And this isn't unsubstianced, I'm speaking from experience. I've answered these questions over and over again. It's already annoying to get the NVidia stuff set up reliably, find new software and adapt your workflow. And the switch from X11 to Wayland broke things like screen sharing/recording, anyways. And we're now piling 20 other things on top, to learn and do manually if you happen to be one of the users who don't use the default standard setup.

And nothing of that is "bad" or can't be fixed... We're making progress with all of that. And we'll get there. All I can say with my experience helping people with their Linux woes and the current state of Flatpak: The "use Flatpak for everything" mentality is causing issues for some newer users. And experience shows: They rarely understand the consequences but heard the hype about Flatpak. And few of them can explain why they used Flatpak over the proper packages in their distro.

So my opinion in short:

• Flatpak is nice : yes
• try a Flatpak first, then the distro package if it doesn't work: hard no
• you can get recent software on older distros with flatpak: yes
• you can recommend Flatpak: Yes, if you also explain the consequences of the sandboxing and pulling things from potentially unreliable third-party sources. You're doing people a disservice if you don't.
• some of this will change in the future: yes
• we should have more sandboxing: yes