70mm is 2.2:1 with spherical (what you call "flat") lenses, which is very very close to the 2.39:1 of anamorphic 35mm. So anamorphic 35mm films are shown "flat" in 70mm.
Anamorphic 70mm is 2.76:1 (Ben-Hur is the best example I can think of), substantially wider than anamorphic 35mm.