“To each their nature” IMO would be interpreted as the diet designed for a particular species. Like the diet of a lion is meat and the diet of a cow is grass, etc. and that is their nature (biologically) and can’t be changed. I don’t know much about Rama at all, but an article by a well-respected scholarly Vaishnava devotee says that there is no confirmation at all in Ramayana that Rama ever ate meat and there are a lot of verses that indicate that he did not like meat eating. I think time and time again in all religious texts, meat eating is never the ideal and there are almost always restrictions placed on it whether it be the type of animal, how it should be killed, and various other rules that either forbid the use of animal products or make it so restrictive that it would greatly limit its use. I feel like in many religions it is clear that plant foods are the most ideal and can be consumed freely without sin or elaborate rules.