the issue is though is that we have to make sure everything is safe, when passing custom install scripts through bash, in the future it could get hacked and end up running malicious commands, mainly the issue is that it just fetches and runs a script, which sometimes people blindly run these
What Flatpak also does well wasn't mentioned, which is sandboxing applications (can snap do this as well i think), I use proprietary applications on flatpak sometimes so i can feed them the resources they only need, like discord, it does not need to see my files or my running processes for the running games feature, so i just restrict them with flatpak. Sandboxing is nice for proprietary software basically, or software that collects info or just any software that connects to a server, you can snip out useless stuff you don't need while it still hopefully functions well.