^This is normally my opinion. I'm only level 16 though, so a lot of our junglers suck and truly don't know what the **** they are doing. Also if we have a jungler our solo top will normally lose the turret before 10 minutes is up. So it isn't even worth it to me, at this point in the game.
In the early levels, it does seem kind of detrimental to have a jungler. But ss you progress, you'll run into fewer duo top situations. You'll also run into more games where a team with a jungler will properly press their advantage against a team without one and the benefits becomes more clear.