This is one topic where people will have a different opinion for different reasons - different people may interpret any situation differently, fans cannot accept their favorite is dumb, it also depends whether they are called dumb based on the current track only.
As for me - I do not find Narendra dumb. For whatever little is known about him, it appears that he never had respect of his wife and he is trying to prove that he is capable of doing something for her, he believes her and does not suspect that she is at fault. He will pay dearly for this blind trust.
Shiv and Jagya are behaving like typical TV leads in the current tracks. Our TV leads are so innocence that they will ignore even the obvious signs of a bad person and believe any sob story. They will continue to help the bad person (thinking that he/she is suffering or is a good person) until one fine day - they discover the hard truth the hard way - drama at its peak - being accused for something they did not do.
But comparatively Jagya is doing better than Shiv in current track. He does not have enough evidence to suspect Shyamal baba (except for Ganga's words) and is feeling indebted to him because DS got rid of her guilt thanks to the baba.
Shiv is almost dumb - no amount of saying that he thought he is helping a tortured woman/this is his goodness etc. will vindicate his actions in the current track. Even if he has not seen a woman like Rasika (for a 30+ man who has seen people from a village, city and even a foreign country - it is next to impossible that he had not seen/heard about such women), how he could buy the sob story ignoring the obvious signs of a cheap woman? How could he forget that he is not a relative/neighbour that he has to console physically, how he could forget that he is the boss and does not know much about the lady, who is a subordinate and he should keep his distance? How he forgot the protocol to inform police when he saw the beating marks on the lady's back?