Dude, even before Michael Holt was created, Mr. Terrific was a character and concept that DC had left moribund and neglected for decades, not just years. They killed off Sloane in a JLA/JSA team-up, and didn't even bother to depict the story of the JSA trying to bring his murderer to justice. It took fans of John Ostrander and Tom Mandrake's "Spectre" book in the 90's writing in and begging them for years to do a story about the Spirit King being brought to justice for that tale to finally be told.
And honestly, fans have forgotten that Michael Holt as the new Mr. Terrific being any kind of fan favorite, let alone a hero positioned to be of any importance within the DCU, was not a sure thing when he was first introduced. Holt could have easily been ignored and forgotten by DC and the rest of its creators. His handling after the "Spectre" title ended could have easily been So. Much. Worse. if somebody who wasn't actually interested in the character got their hands on him before the relaunch of JSA. He could easily have been made cannon fodder in some big event, or even just ignored altogether.