Now let's not kid ourselves. Fighters (pure Fighters) that were Dexterity-based were completely ineffective in 3.x. Their damage levels were very non-threatening. Most of your Spring Attack-type light Fighters had levels in another class, such as Rogue, Scout or Duelist.
You HAD to multiclass to be an effective light-armored warrior in 3.x. At worst, 4e will be no different.
But wait! 4e has Class Training feats, which will let you pick up some of a class' abilities without actually multiclassing, and you don't lose a step in your single class, should you wish to stay so.
And since characters are probably going to get a lot more feats in 4e, what this means is that pure Fighters who want to be light-armored warriors can take some Rogue Training or Ranger Training feats.
Also keep in mind that Fighters have all the weapon-based tricks in their power lists, so you can bet he'll be able to do some things with a rapier that a pure Rogue or Ranger won't do (unless conversely THOSE classes take Fighter training feats).
So, in conclusion:
3e light "fighters": Fighter/Rogues, Fighter/Scouts, Swashbucklers (again, different class), builds revolving around the Duelist prestige class.
4e light "fighters": Fighters taking Rogue or Ranger Training Feats, or conversely, Rogues and Rangers who take Fighter Training feats.