If you only rank a single candidate, there's zero benefit, you're just throwing away the rest of your vote. It's not giving that candidate any extra influence, the way it would in approval voting.
"Vulnerable to bullet voting" is the same thing as "violating the later-no-harm principle," which means that some forms of ranked voting are vulnerable, while others aren't.
- Borda Count is vulnerable to bullet voting, for the same reason as Score (giving points to anyone other than your first choice makes it less likely that your first choice wins, because it increases the score of your second and third choice).
- Condorcet systems are vulnerable to bullet voting, because the ordering of your second and third choices can potentially change who the Condorcet winner is.
- Instant Runoff is "immune" to bullet voting because the ranking of choices beyond the highest non-eliminated choice are ignored. This is also directly responsible for it being vulnerable to the spoiler effect, which makes non-bullet-voting pointless (any vote you cast that isn't for the candidate you expect to win is a waste of time, even though it technically doesn't harm you).
https://clayshentrup.medium.com/later-no-harm-72c44e145510
for instance, alaska just elected peltola even though begich was preferred to peltola by a large 5% margin. palin voters preferred begich to peltola 10-to-1. but IRV ignored their 2nd choices. therefore they would have been better off strategically ranking begich as their favorite.
whereas with approval voting, once they cast a strategic vote for begich, it's safe to approve palin (and anyone else they prefer to their lesser evil). this is, in a nutshell, why score voting and approval voting (rated, not ranked, methods) are so superior. this is social choice theory 101.
https://electionscience.org/commentary-analysis/rcv-fools-pa...
STAR voting is shown to outperform virtually all other methods with any mixture of honest or strategic voters.