I went to install some software today (Gradia) which is only available via Flathub apparently, the install size is larger than my distro which feels like a bit much for a screenshot tool. What’s the deal with the massive size of Flatpaks and is it really worth all the extra space? 4GB per application?

Have you ever tried to install a package and the install failed because of a missing dependency? You spend time chasing down that specific dependency, you find it and try to install it, but then the dependency itself fails to install because of a further missing dependency of its own. This is two steps into “dependency hell”.
This doesn’t occur with a Flatpak install because all the dependencies are baked into the Flakpak.
Thank you, that hasn’t happened to me in some time, but I understand how Flatpaks avoid that now.
I am going to consider myself lucky as I have never run into that in 15 years.