AppImage solves the packaging problem in a bad way (ugh, loopback mounts), but does not solve the dependency problem, try run AppImages compiled for Ubuntu on Fedora..
The main use case for appimage imo is things you just want to run once quickly and easily. Trying beta builds from github releases for example. It's quite poor for anything you frequently use or want to keep updated. It's also completely lacking security iirc which Flatpak does well.
