While Cuomo would obviously go all-out for Hochul, Samuels would have much greater appeal to voters in a Democratic primary than the conservative Hochul, who's already been trying to walk back her anti-immigration views and still has giant flashing neon "A" rating from the NRA to deal with. What's more, Hochul's from Buffalo whereas Samuels is from New York City, where most primary votes are cast, so a Samuels victory would not be out of the question.
And if he were to win, it would create a terrible complication for Cuomo. He and Hochul have already been nominated by the Independence Party, a mostly fake organization that typically sells its appealingly named ballot line to the highest bidder. But under New York's fusion voting system, ballots cast for a Cuomo/Samuels ticket on the Democratic line could not be consolidated with those cast for Cuomo/Hochul on the Independence line, meaning Cuomo would have to spurn the IP (and Hochul) and encourage people to vote for him as a Democrat. That in turn could lead to the IP failing to get the 50,000 votes it would need to stay on the ballot for the next four years, a nifty bit of collateral damage.
More importantly, a Samuels victory would mean that Cuomo's second-in-command would be a fierce detractor of his. New York's lieutenant governorship is traditionally quite powerless, and Cuomo would do his best to marginalize Samuels. But Samuels would still have a pretty prominent perch from which to criticize Cuomo from the left, and the press would probably enjoy covering such a searing, ongoing schism.
Indeed, Samuels could become the pole star to New York's progressive movement, which is badly in need of one. And Andrew Cuomo would have an unceasing problem on his hands for the next four years. What's not to like?