Agree w/ you. From day 1, the actress chosen to play Rukmini was a disappointment, and now, Rukmini herself being sidelined is hard to fathom. Wonder whether they are auditioning Priya's replacement.
Jambavati was major in the sense of her sons. I knew of only 2 of Krishna's sons - Pradhyumna and Samba. A third - Charudeshna - I thought was son of Satyabhama, but he was in fact Rukmini's 2nd son. At any rate, the only sons of Krishna one hears of is Pradhyumna and Samba.
Pradhyumna of course is famous - @ birth, he was kidnapped and a whole story was there b4 he returned to his parents w/ Mayavati, his wife. He was also a great student of Arjun's and a friend of Abhimanyu and Satyaki.
Samba, who was Jambavati's first son, was the other, more infamous son - he disrupted the swayamvara of Duryodhan's daughter Lakshmanaa, and caused the destruction of the Yadavas by appearing as a pregnant woman w/ some of his friends b4 Vishwamitra, Durvasa and Kanva.
Krishna's other sons are far less known. He's known to have had 10 sons and 1 daughter from each of his wives (I'm curious as to whether his 16,100 other wives also had as many children, or maybe less). Since the texts are somewhat nebulous about them, all those stories about other wives for Pradhyumna or Anirudha may well have been about other sons of Krishna.
Shrimad Bhagvatam doesn't seem to sequence the chapters according to chronology, and so some appear totally out of sequence, like the killing of Rukmi, or the marriage of Anirudha & Usha. I do hope the Sagars have worked out the chronology here - if they show Balarama kill Rukmi early, and then later show Rukmi approaching Arjun and Duryodhan to join their sides, it'll look plain ridiculous. Pradhyumna was around when Shalva invaded Dwarka, and therefore definitely around during the time of Krishna killing Sishupala, so b4 they go to the Pandavas and Krishna helping them build Indraprastha, I dearly hope they show the birth, kidnapping and return of Pradhyumna. In b/w these events, maybe they can show Krishna be @ Draupadi's swayamvara, and his adventures w/ Arjun in Khandavprastha. Then, b4 Yudhisthir's Rajasuya yagna, show Pradhyumna return.