Same app in native format: 2MB. As a flatpak: 15MB. As an appimage: 350MB.
Appimages are awesome, rock solid, and I have a few on my system, but flatpak never gave me any problem and integrates better with my KDE, and is smaller. Both have their advantages tho. I'm fine with using both. If you are a developer, make a flatpak or an appimage i dont really care just make your software available for linux. Both are fine, choose the one that fits your specific app the most.
But I also think appimages deserve the same attention and great integration with the OS as flatpaks. Stuff like that AppImageLauncher functionalities should just be integrated inside the DE itself.
But we need an universal package format for linux asap. Flatpak is on the front in this race, and I'm fine with it. Appimages second, for sure.