Epcot officially broke ground on October 1, 1979 and officially opened October 1, 1982. Most of the opening day attractions (save for Horizons and JII) were open by the end of the year. (Imag opened March of 83, and Horizons opened October of 83.)
If memory serves, walls started going up in October 2019. So, if you take 2 years out for major COVID restrictions they will have redone the center in the same time it took to build the entire opening day park.
Even adding in Cosmic, Remy and JoW, they will have effectively built those 3 plus the center in that amount of time.
By comparison, 1979-82 built:
-SSE, Energy, WoM, The Land (4 large slow-moving attractions with 3 theater attractions. Then 2 large slow moving attractions plus an additional theater attraction within a year.)
-CommuniCore East and West with Stargate Restaurant, Centorium Shop and another cafe (forgetting the name) plus the Fountain of Nations
-All of World Showcase, minus Norway and Morocco (1 boat ride, an animatronic theater show and 3 theater shows
-a smaller nighttime show started in Late October, replaced by a bigger show in later 83.