It's true that there are many similarities between Greek and Roman art, but one thing that was very important to the Romans was that there was a distinction between the two cultures. The Romans didn't want to rely on the the Greeks, they wanted to make a name for themselves. This distinction can be seen in the differences between the portraits of Greece and Rome.
Take a look at this Greek portrait of Alexander the Great. We see a very handsome man indeed. There's a dreamy look in his face, an ideal man. Why? Greek artistic conventions expressed ideas about what the ideal person should look like. Perhaps Alexander didn't look exactly like that, but that's what Greek conventions made him look like. The important thing to take out of this is that this portrait shows an idealized image.
Now let's shift our attention to a Roman portrait:
Here we have what looks like an extremely detailed, extremely realistic depiction of a Roman man. One will immediately think that this is a stark contrast to the idealistic style of the Greeks. It's true that differences between the Roman style and the Greek style exist, but they are similar in ways you may not expect.
I learned that there is a style called verism. With this style, artists seek to include super fine details quite meticulously. This is apparent in the wrinkles visible on the subject's face. So you might think that because of this, the artist is depicting the subject in the most realistic, accurate way possible. This is not true.
Verism was the convention of the Romans, just as idealism was a convention of the Greeks. Rather than portray people realistically, they portrayed them with as much detail as possible in order to express the unique Roman values of wisdom, maturity, and service to the state.
So luckily for this guy, he probably didn't actually look like that. Rather, through this portrait, the sculptor is showing that the subject bears the ideal Roman virtues. Artists did this so frequently that it is nearly impossible to distinguish between who is who -- everyone pretty much looks the same as a result of the conventions.
I thought that was really interesting!