Patterns work in one direction. Patterns are not aliases for the collection of packages. If pattern A requires package B, then installing A will also install B, but removing A will not cause B to be removed (it is perfectly legal to remove pattern but keep installed packages).
There is no straightforward way to request removal of all packages that (would) have been installed due to installation of some pattern.
There is no perfect solution to undoing installation of pattern gnome, but the following is close to one: zypper rm --dry-run --clean-deps ‘gnome-*’ removes 309 packages vs 319 packages being installed previously.
Then leave it as it is. Many have four or five DEs installed and their users only use one or two of them. I guess there is a lot more software you never use. when you want to get rid of that “as being bloat”, you better reserve a considerable amount of time and effort for it.
Normally a desktop software install does not really eat much space when you have the recommended minimum size for your root partition and when you have application data (like databases, web-sites, etc.) and user data on other partitions.
But of course do know nothing about your mass-storage set-up.
Oh yes, isn’t that including /home nowadays? Not my favorite because users can then fill up the / partition (mostly unintentionaly by some mischief). blocking the whole system. But that I my personal feeling.