Rhino was one of the many Hulk villains at first, but aside from occasional knock backs and instances of hurting him, he never really overpowered nor defeated him.
As time went on then, he started losing more frequently and blatantly more against him and other characters in Hulk's orbit such as Doc Samson, She-Hulk and Abomination, as well as other powerhouses like Namor. There are also clear instances of Rhino being far below him, such as an issue in which Abomination states he would stand no chance against Hulk in a direct confrontation, or another time where one of his charges didn't even move a serious Hulk, DBZ-style, so to speak.
I would also argue that Hulk's scaling should be handled carefully, not only because of his varying strength, but also due to the long list of people who battled him, to such a extent that you may end up doing a 5-B bargain sale.