One of the most impressive things about top players is their machine-like proficiency - they make even difficult shots with such seeming ease and consistency that they make it look easy. They are like well-oiled machines. This is why coaches have players do so much rote practice, practicing their strokes and footwork until they can do them in their sleep. All players should strive for this mechanical proficiency.
At the same time, you don't want to have the dreaded case of being "too mechanical." This means that you have seemingly perfect strokes, but don't adjust to variation well - and so make many mistakes if the opponent varies his shots. Ironically, this is almost the opposite of mechanical proficiency!
There really are two things here: having perfect or near-perfect strokes that you can repeat over and over against predictable shots, and being able to adjust to variation. You need both. (There are also players with bad strokes but who can adjust to variation - and so they tend to be consistent but their shots are not as strong, or they lose consistency if when they play aggressively or when forced to play at a fast pace.)
How do you develop both mechanical proficiency and consistency against variation? This will sound rather obvious, but you do so by practicing. Many players only do rote drills, where every incoming shot is predictable, and so they develop mechanically perfect shots as long as the opponent is predictable. You need to also do match-type drills, where you add variation to the drills and so have to adjust. There are zillions of possibilities. At its most basic, simply serve and attack, where your partner varies his returns. You may have some restrictions, such as he has to push long anywhere, or he has to perhaps push short or flip to a wide corner, or perhaps flip anywhere. Think about what happens in matches, and work out drills that match your game and what you need to adjust to.
One reason for becoming too mechanical is playing the same players over and Over and OVER. You get used to them and only them. Instead, you need to play tournaments and leagues where you play different players, where you are forced to adjust to different styles, strokes, and techniques. It's not a matter of learning to play every style, stroke, and technique - it's a matter of learning the habit of adjusting.
The ultimate goal is to have true mechanical proficiency, against any type of variation - like the top players. Because that is "good" mechanical play - and will turn you into a true table tennis machine!