You need to be a bit careful with statements like that. There’s very strong evidence that the stacking effect linearizes at high stacks like 4-1 or 5-0. But the same is not true for added defense on a single hero.
Further, the 20% defense boost for defenders magnifies the +Defence gained through emblems. The number of tiles required for a kill will likely get worse, not better, for color stacks with emblems against tanks with emblems.