Optional crash reporting was merged. Most of the backlash in the PR is about the significant dependencies (Google's BreakPad) which were pulled in with it.
However, by default Audacity isn't built with it, you need to specify a CMake with the URL to send data to. No distros that I know of enable reporting.
Judging purely on the dependencies I see in pacman, nsxiv depends on imlib2, which pulls in a lot of libraries, while imv links to a subset of those libraries directly.
Others have mentioned disk usage and desktop integration. There is some truth to them, but shared runtimes keeps disk uasge down (although worse than native apps). Desktop launchers now search /var/lib/flatpak/exports/share/applications by default, but I'm still having issues with themes in one or two niche apps.
Trust is the big one. The benefit of your distro's packages is that they are maintained by a limited number of maintainers. Flatpaks have a much, much larger number of maintainers, which is where sandboxing comes in. Flathub now marks apps with lax permissions as "potentially unsafe", which is a huge step in communicating this to the average user.
Most desktop apps can get away with having next to no access, as long as they support the appropriate XDG desktop portals.
Ultimately, your mileage will vary, as there are many classes of application which are ill-suited to being sandboxed. Program launchers, programming languages, IDEs, file managers are a few.
I grew up with Fahrenheit, but switched my weather app to use Celsius for a while, and I've internalized it pretty well. It works fine. The "human experience" angle doesn't work anyway because that experience is very locale-dependent.
Optional crash reporting was merged. Most of the backlash in the PR is about the significant dependencies (Google's BreakPad) which were pulled in with it.
However, by default Audacity isn't built with it, you need to specify a CMake with the URL to send data to. No distros that I know of enable reporting.