I don’t understand what problem they are meant to solve. If you have a FOSS piece of software, you can install it via the package manager. Or the store, which is just a frontend for the package manager. I see that they are distribution-independent, but the distro maintainers likely already know what’s compatible and what your system needs to install the software. You enjoy that benefit only through the package manager.
If your distro ships broken software because of dependency problems, you don’t need a tool like Flatpak, you need a new distro.
Every single distro maintaining their own version of every single Linux app is just a lot of work that wouldn’t need to be done if there was a way of making a version that worked on every distro out of the box. Plus that way app devs don’t have to worry about trying to hunt down every weird bug that only comes up occasionally while doing a specific thing using a specific version of a specific library that only one distro uses.
None of them are better than a well maintained native app from your distro. In fact, realistically they kinda have to be at least a little worse than an actually well maintained one. If you include all the time spent maintaining native apps, universal formats are potentially orders of magnitude less work to maintain if they become the default though, and that is valuable. Valuable enough that a lot of the people doing that work are pushing for them pretty hard.