What about Laas then? He apparently never came into contact with the Founders, and didn't even know much about them until he met Odo, yet he was capable of taking shapes which Odo had apparently never even considered, and all through his own periods of trial and error. I agree that not knowing the Founders would reduce Odo's potential for growth (no pun intended
), but I'm not sure the odds would be so high against him.
I believe Laas became aware of what he was years (eons?) before Odo knew. If you watch Children of Time you'll see that Odo is a much better shapeshifter then.