It’s one thing if you’d be busy with the Mitzvas Assei of Ve’ahavta Larei’acha. But your main point is that these Mitzvos are there for the same reason the Greeks preached them.
Ono’as Dvarim is not a De’oraisa, but I can agree that it’s not a good example because it would be a Lav She’ein Bo Maasa.
Hashavas Aveida is the Din, it is not a just another implementation of being a nice guy. In fact the laws of Hashavas Aveida contradict don’t follow through with the rules of being a nice guy. Chazal had to say that there is also the other, general, point of doing what is right, and we return even what wouldn’t have to be returned according to the Halacha.
Therefore, if it wouldn’t have been a Din Torah, it wouldn’t be written out in the Torah. It would have been one more thing we would do as part of Ve’asisa and Ve’ahavta.