Plant fats consumed with their respective plants are probably tolerable, because your stomach has limited volume. Only after they are squeezed out do that you can have oil out of 20 kilos of plants in each single meal then it might not suit your body.
So let me restate the question.
Do you any plant fats that were extracted from plants before industrial age and used as a staple meal ingredient by themselves?
Olive oil is one. Is coconut oil the second? What else?
Probably? Coconuts were certainly cultivated and used in prominent societies dating back to 1500 BCE or earlier, and the oil has been used for nearly as long, although it's unclear to what extent this was for culinary purposes.
https://en.wikipedia.org/wiki/Coconut#Origin
> Were people there healthy and not unusually prone to various diseases and not overweight? In some island nations being overweight was beneficial for travel and times of scarcity. So tradeoffs of their diet might not fit us so well as it fitted them.
This is also unclear, although I assume the same ambiguity applies to animal-sourced fats which were consumed in cultures very different to our own.
Secondly, does the world in which this argument exists consist only of the west? Your mention of olive oil as the exception and a “western diet” seems to indicate so given that plant fats (such as in nuts or coconut oil) have been consumed for thousands of years. Would any of this generalize to humanity?