Can lokuttara citta's be defined as the true knowing essence (yathabhuta nana dassana)? Can lokuttara citta's be defined as the true knowing essence (yathabhuta nana dassana)?
No, yathābhūtañāṇadassana is said to refer to early stages of Vipassana insight:

yathābhūtañāṇadassananti yathāsabhāvajānanasaṅkhātaṃ dassanaṃ. etena taruṇavipassanaṃ dasseti. taruṇavipassanā hi balavavipassanāya paccayo hoti.
yathābhūtañāṇadassana refers to that which is understood as knowing things according to existential characteristics (sabhāva). By this is meant weak (taruṇa) vipassana. And weak vipassana is a requisite for strong (balava) vipassana.
-- SN-a 2.1.3.3

The commentary here is explaining a passage showing the following progression:


avijjūpanisā saṅkhārā - formations have ignorance as a cause

saṅkhārūpanisaṃ viññāṇaṃ - consciousness has formations as a cause

viññāṇūpanisaṃ nāmarūpaṃ - mind and body have consciousness as a cause

nāmarūpūpanisaṃ saḷāyatanaṃ - the senses have mind and body as a cause

saḷāyatanūpaniso phasso - contact has the senses as a cause

phassūpanisā vedanā - sensations have contact as a cause

vedanūpanisā taṇhā - craving has sensations as a cause

taṇhūpanisaṃ upādānaṃ - clinging has craving as a cause

upādānūpaniso bhavo - becoming has clinging as a cause

bhavūpanisā jāti - birth has becoming as a cause

jātūpanisaṃ dukkhaṃ - suffering has birth as a cause

dukkhūpanisā saddhā - confidence has suffering as a cause

saddhūpanisaṃ pāmojjaṃ - delight has confidence as a cause

pāmojjūpanisā pīti - rapture has delight as a cause

pītūpanisā passaddhi - tranquillity has rapture as a cause

passaddhūpanisaṃ sukhaṃ - happiness has tranquillity as a cause

sukhūpaniso samādhi - concentration has happiness as a cause

samādhūpanisaṃ yathābhūtañāṇadassanaṃ - knowledge and vision of things as they are has concentration as a cause

yathābhūtañāṇadassanūpanisā nibbidā - disenchantment has knowledge and vision of things as they are as a cause

nibbidūpaniso virāgo - dispassion has disenchantment as a cause

virāgūpanisā vimutti - freedom has dispassion as a cause

vimuttūpanisaṃ khayeñāṇaṃ - knowledge of destruction (of the taints) has freedom as a cause.


-- Upanisa Sutta (SN 12.23)

Balava vipassana refers to nibbida. The lokuttara magga and phala cittas are equated with viraaga and vimutti respectively.