Baseball is cyclical. Much like this hobby, players come and go, public interest ebbs and flows. For a period, I'd imagine Donn Clendenon was a fairly well regarded name among baseball fans.
He didn't break into the majors until his age 25 season in 1961, just missing the Pirates World Series season, and wouldn't see regular playing time until age 27. He would put up solid seasons leading up to a breakout .299/.356./520 in 1966. But at age 30, the breakous undoubtedly came with a grain of salt.
Declining numbers in '67 and '68 left him unprotected in the Expansion Draft, where the upstart Expos snagged him. His career would continue to trend downward until yet another surprising season in 1970 that netted him MVP votes at age 34.
But the next two seasons would mark dramatically decreased playing time, and would be his final two in the majors.
I honestly don't know how you'd qualify a player like this. He isn't a flash in the pan, putting up two exceptional seasons and some very strong years early in his career. But clearly he lacked the consistency and star power to become a major name. Instead, his two standout seasons come nestled among a career of downward trending replacement level play.
But I guess sometimes baseball is just strange like that.