It's true that telling people to fill their ballot would go a long way towards avoiding this problem, but it's not perfect. An "uncapped" RCV system in theory entirely avoids the vote splitting concern, but I think there's a residual issue due to NYC's 5-candidate cap.
Imagine there's a set of voters who would all prefer Lander, Mamdani, Myrie, Ramos, Stringer, and A. Adams to Cuomo. If half of them rank in that order (with Adams unranked), and the other half do the same thing but flip Stringer & Adams, half the ballots will be exhausted before the final round.
yeah, and even though i think his ego will prevent him from doing it, this is one reason why stringer should drop out and tell his voters to throw their support behind Lander and A. Adams.