Direct answer first: Historically, Melbourne Cup favourites have not won very often. As of recent decades, only a minority of favourites have saluted, with the last favourite to win being Fiorente in 2013. Before that, Makybe Diva won as a favourite in 2005, but since 2005 only a small handful of favourites have prevailed. Overall, roughly one in six to one in seven favourites have won across the long history of the race, with many years producing upsets or near- misses. Context and nuance

• Early history: The first Melbourne Cup in 1861 produced a major upset when the favourite Archer defeated Mormon, setting a long-standing pattern of surprising results in big-field handicaps.
• Contemporary trends: In the modern era (roughly since the 2000s), favourites have not often won; for example, the 2013 win by Fiorente stands out as a relatively rare example of a favourite prevailing in recent times.
• Betting context: The common adage around the Cup is that it’s a bookmaker’s race due to the large fields and variable conditions, which tends to dampen favourite success rates compared with other major races.
• Notable exceptions: Makybe Diva’s three Cup wins (2003–2005) included a year (2005) when she started as the favourite, illustrating that top-rated horses can win, but such occurrences are exceptional in the modern era.

If you’d like, I can compile a precise year-by-year breakdown of Melbourne Cup favourites and their finishing positions, or compare the favourite win rate over different eras (e.g., pre-2000 vs post-2000) based on reliable race histories.