Lego is well suited for building the same things that you would build with bricks such as houses and buildings. Lego technik or Mindstorm tries to expand on that by offering pieces which connect in a similar fashion as Meccano by having regularly spaced holes in the bricks.
A downside to that is that pieces can only be connected at fixed points. Fischertechnik pieces on the other hand may be connected at any point. A standard building block can connect to another standard building block at any of the block’s six faces. That gives versatility which can not be matched by either Meccano or Lego. Fischertechnik well suited for constructing machnines but poorly suited for making things resembling builds. Lego is better suited for this.