i also recite the same dua-e-Qunoot without saying "Kullahu" in the middle. but why do they have "Kullahu" in middle? what does it mean?
and what is the importance of dua-e-Qunoot?
it emphasizes/qualifies "al-khair" ... in the context of the dua it means we turn to Allah for "All" (Kullahu) good things/blessings (Al-Khair). Since it is a qualifier, I suppose there isn't much harm if someone has been reciting the dua without the word, but Allah knows best.