It makes the signal stronger in the target location, but the antenna is still very Omni-directional. It's just using extremely small signal offsets between transmission antennas to optimise the amplitude of the signal in the area of the receiver.

Directional antennas can still very much help, as well as wave guides to push more signal in the desired direction (sacrificing signal in another, potentially undesired or unrequired direction).

Source: over 10 years in IT with a focus on wireless network technologies.

It gets really interesting when you get into mimo and multi-user mimo, and the system is transmitting on the same channel to multiple endpoints at once, with different data for each. Shit is crazy.