I fully agree w/ you. There was no need to show the Ramayan - a story where Mahadev plays at best a cameo role. Same for the Mahabharata - both the epics might have place in a Vishnu centric serial, but not this one.
I was enjoying this serial b'cos it was a welcome break from the epics. While a lot of the Sati story was fictional, they showed her end beautifully, and established what might have been a standard, had they followed up. They covered the introduction of Parvati well, and aside from the blooper of having Tarakasura there from Sati's time, they covered that well.
Things started going downhill once Shiva-Parvati's marriage was over. First they introduced Shumbha & Nishumbha, and tossed in some meaningless stories b4 a half baked battle that saw only 2 of the asuras - Dhoomralochan & Raktabheej - slain. Then they showed a bizarre account of Kartikeya's birth, and him being raised by the Kritthikas, and then a pretty petulant Kartikeya as he kept growing (in contrast to a perfect Ganesh later). Later, they also spoilt Kartikeya's war w/ Tarakasura by showing Mahadev helping him, when in fact, nothing of the sort happened. Also, in the Mahishashur story, they showed Parvati take Durga's form due to Mahishashur threatening Kartikeya, which was just hogwash.
Essentially, this serial has ruined the depiction of both Parvati & Kartikeya, while showing Mahadev, Ganesh & Narayan(!) almost perfect. That had already spoilt it a lot for me. There are other stories that have yet to be shown - the story of Tulsi, Andhakasura, Ayappa and so on - which are very much Mahadev stories, not covered elsewhere and perfect for DkDM. Instead of covering those, they've dived into a full fledged Ramayan, making things up as they go along (environ-mental Tardka, curious Hanuman, loose cannon Urmila) so that the entire charm of this serial is gone. And that's w/o even bumping Sona, which was really inane from a casting standpoint.