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I hear your frustration. It can be annoying. There's a reason for it, and that's because environment variables are limited in their use by scoping: they're only inherited from the parent to children, and they're pass-by-value. This means that, from a child process, you can't influence the variables for any other sibling, or the parent. There's no way to propagate environment variables to anyone except new children you fork.
This is a significant limitation. There is no work around using only environment variables. It's a large part of why applications store scalar values in files: it's (almost) the only environmentally agnostic way to propagate information to other processes.
Herbstluftwm has herbstclient getenv and setenv, because ostensibly every user process is a child of the window manager, and it's a convenient way to communicate scalar changes between processes. tmux has similar commands; in both cases, the source of truth is the parent application, not the environment. gsettings is just Gnome's version; KDE has it's own version. I'd be surprised if Sway didn't.
Environment variables are great, but they're limited, and they are simply unsuitable for purposes. They're also insecure: anyone with the right permissions can read them from /proc. The consequence is that it can be difficult to track down where settings are stored, especially if you're still using some component of a desktop, which tend to manage all of their settings internally.
We do have a global solution for Linux: the kernel keyring. It's secure, and global. It is not, however, automatically persisted, although desktops could easily persist and restore values from the keyring when they shut down or start up. Every desktop I know just keeps it's own version of what's essentially the Windows registry.
It's a mess.