But fullborns don't appear naturally, allomantic sDNA interferes with Feruchemic sDNA. Radiants can be produced by the dozen if the spren allow it. A fullborn had to learn how to use all of his abilities and how to combine them without injuring himself, and store and compound all of the attributes. There are maximums of how fast, strong, heavy, etc. a fullborn can go before the magic stops providing them with protection. Radiants can use there abilities almost instinctively. Kaladin did a reverse lashing before he perform any of the other lashings, Lift perform regrowth on the first try when it was almost too late.
Radiants also fight in pairs. There spren can watch for fullborns and change their shape into shields to block the fullborns attacks, they can reform over and over so full norms will have to destroy the spren before taking on the radiant.
The surge of transportation allows the radiant to escape into shadesmar and then transform the land around the fullborns or the very clothes on his back to kill him.