Ultimately, it is not the job of historians, nor the function of history, to create heroes and villains. When historians study prominent individuals, they tend to think about them in the context of broader contemporary events, attempting to understand their actions—and their inaction—in light of these events. What often emerges are complex and nuanced portraits of human beings, who made mistakes, did bad (sometimes awful) things along with things we can assess as beneficial. "Revisionist" is a label that one might apply to any historian who studies a figure that has already attracted attention from other scholars. There is no point for historians in studying any topic if they don't think they have something fresh or original to say about them.
Garvey is a complex figure that has received a great deal of scholarly attention. His public advocacy of black nationalism at the height of Jim Crow was remarkable, but in the years following World War II, he was dismissed by (mostly white) scholars as a sort of crackpot, or even criminal (due to his conviction for mail fraud surrounding the sale of stock in his Black Star Line.) Beginning in the 1960s, however, scholars and especially activists began to view Garvey more favorably. By the 1980s, books like Race First: The Ideological and Organizational Struggles of Marcus Garvey were framing his leadership of the United Negro Improvement Association (UNIA) as crucially important. What has especially interested scholars about Garvey is not so much his struggles with the law, and the collapse of the Black Star Line as his transnational importance. Scholars now tend to frame movements in terms of their international impact and influences, and Garvey, who was an important figure in Jamaica, the United Kingdom, and the United States, in addition to West Africa, is seen as the leader of an international phenomenon of Pan-Africanism. This, in fact, is one of the arguments of books like The Age of Garvey, published by historian Adam Ewing in 2014. Garvey's foibles are seen as far less significant than his involvement in this mass movement.
In short, historians have less interest in framing Garvey as a hero or a villain than in placing him in the context of Pan-Africanism and the many movements, Black Power in particular, that it influenced.