That is correct. Generally there are enough significant changes between releases that some sort of "incremental update" like you're describing would have to contain most if not all of the files anyway. Rather than have multiple installers (one for installing on a system with no MATLAB installation, one for installing on a system with an installation of the previous release, one for installing on a system with an installation from two releases ago, etc.) each release has its own self-contained installer.
Installing update releases generally involves a much smaller set of files which is one reason you could install say release R2022a Update 1 on top of an existing installation of release R2022a.
