Is Sita incarnation of Goddess Lakshmi because Rama is considered to be incarnation of Vishnu?

The concept of Vishnu as the SUPREME GOD with 2 consorts,i.e,  Lakshmi (Sri Devi) and Bhumi (Bhu Devi) cannot be found in Srimad Ramayana. In Ramayana era, the word LAKSHMI was used to indicate riches only, but not as the consort of Vishnu. या हि वैश्वरणे लक्ष्मीर् या च इन्द्रे हरि वाहने | सा रावण ग्ऱ्हे सर्वा नित्यम् एव अनपायिनी || ५-९-८ Whatever wealth is at Kubera, whatever riches at Indra with green horses, all that affluence was at Ravana's house. That wealth was always without reduction." ----------------- Srimad Ramayana was followed by Mahabharata.   And, the Puranas, Srimad Bhagavatam, etc came at much later date. In an attempt to make believe the readers that Sri Rama was in fact an incarnation of Vishnu, many interpolations were added at a later date. In Ramayana era, as in Vedic era, Vishnu was one among 33 Devas, but not the SUPREME GOD, as was described in Puranas.