First of all he is not at all dumb, nave and clueless to everything that goes on. Rather I would say he majority of the times actually is the most logically thinking male lead, as the problem with other male leads is blind faith. All the time male leads have family members they will always believe their wife over or if their wife is shown in a bad light he will instantly come to the conclusion that his wife is at fault. However kunj is the complete opposite as he actually looks at both sides of the coin and most of the time is either impartial or has complete faith on his wife.
There have only been a few times when he lost faith in twinkle and accused her, that too when he felt the self-respect or safety of one of the elders of his family was at stake such as bebe, usha and manohar. Remember after the whole fiasco of anand kidnapping kunj and twinkle, twinkle revealed to everyone that anand was the kidnapper and usha was furious on twinkle but kunj though was shocked and a little mad, he still retained his calm composure with twinkle and said he would give her a chance to prove herself. He did not lose his cool over the issue of twinkle accusing his brother but did when it came to those who he considered parental figures, who are typically kunj's weakness as he is an emotionally sensitive person and attached to bebe and his parents. That is what makes him amazing and sets him apart from other male leads; he actually tries to see and understand both sides of the story and give his wife the chance to prove herself and stands up for her.
He also is not the typically hot-tempered male lead who will lose his cool over the female lead over the smallest of things, rather he knows how to cope with her childishness or mistakes, or try to keep his cool to see the bigger picture when his wife is shown in the wrong. He loses his tempers only when he truly feels his family members are being wronged or when someone else is in danger.