@shiva_linga

Jayasthiti Malla was a Maithili-origin nobleman/panji (high ranking minister then) who married a Malla princess. He was not a Brahmin by birth, if he was he would not have the authority to rule as a Kshatriya king. It is important to understand that although we now think of Malla kings as 'Newar' kings, but the simple truth of the matter is that those Mallas never considered themselves as 'Newar' in the sense that they considered themselves as 'Thakurs' (called Thakoo in lcoal Newari), as outsiders, immigrants to Nepal who came here to rule the local people. The 'Newar' clans of present day which call themselves as Malla, Pradhan, Rajbanshi, Kayastha, among others only 'became' Newar in the Shah dynasty and after the fall of Nepal Mandala to Shah kings. It is also to be noted that the term 'Newar" was (and is still in remote Newar villages) used only for the upper-caste Hindu Shrestha caste only. But that would be a story for another day. Before that, Mallas almost always married princesses brought from Tirhut/Mithila or far western regions and gave their daughters to the ruling nobility of Kathmandu then (most notably called Pradhans.) Even though they accepted the local, indigenous culture and language, they still spoke Maithili in their courts, they brought with them their Maithili culture, gods, traditions among others. This is when as you rightly pointed out, Vedic Hinduism re-emerged and it chipped away the more archaic form of Hindusim Newars followed - Tantrism and Shaktism. If you want to see the influence of Mithila in Nepal Valley and Newars - just go around Durbar Square of Patan for example and you will see Mithila architectures in the form of shikara-vimana architecture, Bhagvad Gita in Krishna Mandir, and most interesting of all, Newar peasant groups (Jyapus, Nai, Kapali) still singing bhajans in Maithili language every morning.

But power is in number, and like I said previously, the ruling Brahmin/Kshatriya elites who came to Nepal Valley and became the Rajoapdhyaya (Dev Brahman) and Chathariya Shrestha (Kshatriya) were a minority compared to the general population and hence Tantrism and Shakitsm could not be completely replaced by the more 'refined' Vaishnavism or modern Vedic influences. This is why all Newars till date are so influenced by blood sacrifices, by Shakti and Devi puja, by almost tribalistic and pre-Vedic worship of certain rituals and Gods, the use of 'pancha makar' - मद्य, मांस, मत्स्य, मुद्रा, मैथुन - in every puja is a must for Newars. And all of this is because Newars like much of eastern India are Tantricist and Shakti worshippers to the core which is an even older version of Hinduism than Nepal's Hill Bahuns profess.