@shiva_linga.

First off, Maithil Brahmins were never 'rulers' in the traditional sense of the word. They were Brahmins as in pujari/purohit. The Maithili speaking Brahmins as you have written yes they held great amount of power, and even till today, their descendants, the Rajopadhyayas hardly even cross 5000 population. So their population 500-800 years ago would have been almost negligible, so their population would have been too inconsequential for them to be ruling elites. Because of the actual low population of Brahmins, we have so many para-priests who acted as priests yet are of lower status and not Vedic Brahmin priests like the Rajopadhyays in the strictest sense. These are Joshi, Rajbhandari, Karmacharya, Bajracharya, Gurubacharya, etc. The rulers (Malla themselves as the various high caste clans that came after 14th century with Malla like Singh, Amatya, Pradhan, Rajbhandari, etc.) were all of Maithili or Rajput origin as in they are Kshetriya, not Maithil Brahmin like you infer.

Jyapus are mainly descendants of the Kiratis and Gopalis and Mahispals. Shresthas are mostly the Lichchavi descendants.

But what you have said other things are true nonetheless.