Enter the current day, where online complaints about input delay are all but a thing of the past. Rollback refers to the netcode structure each game runs their peer-to-peer connections off of. In an ideal setting, rollback netcode would be no different to its counterpart, delay-based netcode. However, these structures tackle the inevitable issue online when data transfered between players takes longer than the game's ability to read it.
Delay-based netcode keeps players connected and in-sync by calculating the amount of frames necessary the game's inputs will delay in order to ensure data is sent properly. Rollback is a new technology structured off of that framework that acts as a predictive model as for what could possibly be animated in the time that was lost.
This overrides the need for a delay on inputs making the games feel far better to play online and translating that gameplay to offline battles. As an example, my best friend from high school moved to Japan two years ago. Despite our near 200ms ping difference in connection, our games together never feel sluggish or as if I have no control.