Yes but that's the default behaviour of git pull so it's expected to fetch and merge when you pull. Changing the default behaviour can lead to confusion or mistakes.
Setting up the rebase in config of a specific branch stay explicit because Git will
If the rebase is not straight forward then you can still abort it.
I would love that git has a config feature to force ff-only on pull but base on what I know you need to create an alias to have `pull --ff-only` replacing `pull`