Essentially yes, if you start using lots if older applications or mixing applications that use many different dependency versions, you will start to use lots of extra disk space because the different apps have to use their own separate dependency trees and so forth.
This doesn’t mean it will be like 2x-3x the size as traditional packages, but from what I’ve seen, it could definitely be 10-20% larger on disk. Not a huge deal for most people, but if you have limited disk space for one reason or another, it could be a problem.
Appimage is probably the most similar to a naked .exe in Windows. They are useful for small apps or simple indie games, but I prefer Flatpaks for my everyday big applications.
Agreed, Snaps are like Flatpaks but worse because locked down back end and Canonical’s sketchy nature. Imagine a really delicious pastry that anybody can make and sell, then imagine the same pastry but only one bakery in the world can make and sell it. Which would you prefer? Lol