As far as I know, mangalsutra is tradionally a maharashtrian & south indian concept, north indians have sindoor as a suhaag ki nishaani. Ekta introduced this thing of all married women wearing both mangalsutra as well as sindoor - otherwise Punjabis, Rajasthanis, bengali, all never wore i!
As much as I have observed, Sumitra, Gehna & Anandi have been shown wearing only sindoor, not mangalsutra...which I think is correct as per rajasthani traditions! Gauri had been given the mangalsutra by Kunda Tai, who was a maharashtrain. Whether or not Gauri continued to wear after she left Kunda Tai house, I don't remember...never observe Gauri so much😆
Now coming to the incident - of course, there is nothing right or wrong - its a matter of your belief. Even my bhabhi wears it only when she wears Indian dresses or when there is any function at home - which is fine by us at home. Jagya made such a big deal out of it bcoz he is going thru a bad phase, an insecure phase. He is right now feeling very inadequate professionally & this increased that feeling of self-doubt.
Personally, I don't have an opinion either ways...but I think Gauri should at least try & put forth her view in a manner more cordial...these days all her sugary talk is a thing of the past!