You sure like your emoticons, don't you?
Odo has a few disadvantages: for one thing, he's young. Although this was no impediment to Laas, it seems like Laas was never under the thumb of a solid. Odo, on the other hand, was pretty much at the mercy of Dr. Mora and the Cardassians for much of his life. Odds are he didn't get to explore his abilities a whole lot under their gentle tutelage. He also hadn't had a lot of exposure to his own kind.
Also, there is no reason to think there isn't some natural talent involved in shapeshifting. Could be he just wasn't naturally that good at it. Laas seemed to be extremely adept, and there were changelings that had no trouble convincingly replacing humans and other solids.