If any script is to run after install - either by the user, or at install time (which I do not believe is an option) - it won’t be able to copy files into vim’s install directory, so here you’d be back to $HOME/config/settings/vim
Unless this is a more massive collection than I imagine, I think the separate package is overkill. I guess that leaves you shipping the vim files in your package’s data, and just notifying users where it is if they want it - I think that’s easier for them than being notified they have to go get another package anyway.
A package is like a read-only union filesystem. My picture of what waddlesplash was proposing, that your filesystem and vim’s could both have /data/vim directories, and both packages’ files would appear there, if both were installed; if vim weren’t installed, yours would be alone there, and vice versa. But that’s awkward because the directory depends on the installed vim version. You can’t go in after the fact because they’re read-only, and anyway that would fall apart at the next vim upgrade.