Instead of doing --all and then trying to filter out the stashes, don’t ever include them in the first place:
git log --branches --remotes --tags --graph --oneline --decorate
The main problem that arises from trying to filter them out afterwards is that if the stash is the latest commit on that branch (because even though it’s not the head of the branch, it’s still the most recent descendant of it), it can actually filter out the entire branch from the log, which isn’t what you want.