Basically grids is a 2D layout system, while flexbox is a 1D constraint system that results in stuff happening on the second dimension. They're complementary and it would be foolish to use one when the other is needed.
No CSS Grid Layout is far, far more powerful and versatile than tables ever were. Certain significant classes of layout problems that were either a major pain or even outright impossible with current CSS tools are about to become fairly straightforward.
