There is a world famous Jewish speaker who believes in Torah Misinai and the like but only keeps the Rabbinic laws that make sense to him. For example, he does not keep Yom Tov Sheini in Chutz La'aretz. Would someone like that be considered a Apikores?
According to the Rambam the category of Epicurus includes those who "dispute [the authority of the Oral Torah's] spokesmen" (Mishneh Torah, Hilchos Teshuvah 3:8). It is very difficult to argue that one who rejects the Rabbinic authority to enact binding legislation in direct opposition to their professed authority isn't disputing the spokesmen of the Oral Torah.