Easier to maneuver, yes. Control, perhaps. Hit . . . the spots between the armor . . .which would be at full arms length from you . . on a moving person . .who is trying to either evade your strike, or hit you himself (likely with a longer weapon) or both - this, I'm not so sure about.

As example, there's a reason why a boxer with a long reach will often (not always, but often) defeat one with a shorter reach. The longer reach allows him to hit the shorter guy before the shorter guy can get in range to hit back. Advancing with a dagger against someone with a sword, you have to be more careful, stay out of reach of the sword, or swing after the sword swings, etc.

Also, your reach pretty much equals your arm length. If you thrust to full arms length, I move back . . you miss. With a sword, reach is longer, so if I'm at arms length, chances of hitting are greater, as you have to move farther to evade.

So I'm not so sure that, in a fight, it's so easy to hit. For an assasination, yes, sure. And yes, you certainly CAN hit in a fight with a dagger. But as consistently as with a longer weapon? Assuming equal skill, doesn't seem to me you would.