Appimages don't bloat the system, they are actually many times even smaller than native packages thanks to their compression (librewolf being 100 MiB instead of 300 MiB, libreoffice being 300 MiB instead of 600 MiB).

And those are "lazy" appimages made with linuxdeploy, if you do some tricks with static linking to can get their size down way way more. For example one case is qbittorrent, their official appimage is 100 MiB while there is a fork called "qBittorrent Enhanced Edition" and they got the size of the appimage down to 26 MiB

I also don't know what you mean by security risks with the libraries, the appimage gets made in CI (usually ubuntu 20.04 or debian stable) and the libraries from those distros get bundled and released, the only way this could be a security risk is if the whole appimage is outdated or debian/ubuntu haven't caught to updating their distros.

My big issue wiht flatpak is that they don't follow the xdg base dir spec and neither add the binaries to PATH (And they said that they will not fix those issues btw), making them only useful for some graphical applications, while pulling several gigabytes of runtimes and dependencies, and the more I've been using and understanding appimage the more I think both flatpak and snap should have never existed. As 99% of what they do could have been done with appimage already and just keep a centralized repo of approved appimages for security concerns.