I would replace Calzaghe with ODLH. Oscar had a much bigger impact on the sport and accomplished more. In fact, Oscar helped make Pacquiao and Floyd the stars they became.
Twenty years: Pac, Floyd, RJJ and Wlad. (Alternate: Pea) Alltime: Ali, Robinson, Langford, Greb. (Alternate: Duran) Any Mt Rushmore of boxing that did not include Ali you would be struck asunder by way of a thunderbolt from on high.
All time Rushmore: Robinson, Armstrong, Duran, Ali Last 20 Years: Pacquiao, Roy Jones Jr, Whitaker, Mayweather
I won't do last 20 years because Mt. Rushmore is an all time monument. . . .so here's my all time monument of boxing. Muhammad Ali, Joe Louis, Sugar Ray Robinson, Rocky Balboa
Last 20 years: Barrera, Martin Castillo, Nate Campbell, Lomachenko All time: Barrera, Duran, Jofre, Canizales Current: Lomachenko, Khytrov, Mikey Garcia, Inoue
What are you asking here? p4p best of the last 20 years, or personal heroes? If the latter, then: Mikkel Kessler, Israel Vazquez, Cristian Mijares, and MAB.
Personal heroes makes sense. Isn't the purpose of Mt Rushmore to canonise 'patriotic American heroes' more than celebrate the 'greatest presidents'? The guys I listed are the boxers who are most what I love about boxing.