You've just misunderstood what a controller is.
The PHB explains it on page 16:
Controllers deal with large numbers of enemies at the same time. They favor offense over defense, using powers that deal damage to multiple foes at once, as well as subtler powers that weaken, confuse, or delay their foes.
I didn't see anything about push, pull, or slide there.
A controller isn't about moving enemies around; it's about what MMOs call "crowd control" -- that is, delaying and disrupting enemies so that the heavy hitters only have to deal with two or three at a time and don't get overwhelmed. D&D adds an extra element with the use of area spells versus minion (who tend to overload a defender's stickiness through sheer numbers).
A wizard fulfills that role not by shoving people, but by having lots of effects that cause slow and immobilize, knock enemies prone, and create difficult terrain. A wizard can't lock enemies down like a defender can, but he can slow them down so that the defender-striker side of the team don't get swarmed, or put up walls and clouds to stop the back line from being able to effectively attack past the brute squad.
Against a single enemy, a controller is a lot weaker; his main role there is just to throw damage and try to hamper the enemy as much as he can. Thus, wizards also have access to a number of single-target disruption spells, like Ice Tomb, Disintegrate, or Mesmeric Hold, which can take one tough enemy and stop him from just rampaging around at will. (Note that a lot of those spells, like Mesmeric Hold and Force Volley, give you an option to work more effectively on one target, or spread out to hamper a group, thus allowing them to fulfill both halves of the wizard's job.)
One blogger noted that a controller who does his job right will probably rarely get recognition for it. He's not very flashy with his purely mediocre damage numbers, and it's not easy to see the turn-to-turn benefits of dropping Slow on a half-dozen orcs or making the bad guys go around a big patch of ice (or fall down in it). The fighter will get cheers for taking out an ogre with one axe critical, but they typically won't notice that without your intervention, the swarm of goblins would've sneak-attacked the cleric to death. The controller "wins" when he forces the enemy into a bad strategic position -- that is, by stopping potential problems before they start. And you rarely get kudos for things that didn't happen.