Dean Winchester is infinitely stronger than Cain. Cain, who lived with the Mark for centuries without letting it fully consume him until those last few months of his life... But Dean was stronger. Because for all the times the Mark challenged Dean's control- cracked it even- he still had the strength Cain never possessed. Dean was strong enough to save his family from himself. In all those hundreds of years, that was the one thing Cain never could do.