The Hellenic influence over the broader Mediterranean world, from Spain to Syria, was so great by about 300 BCE that it touched all cultures, Rome included. Just as American culture today is so powerful that you can find McDonald's restaurants and Hollywood movies in almost every country, Hellenic culture dominated in its time. As such, to say that Roman art is late Hellenistic is not inaccurate. Roman copies of many Hellenistic works have survived, such as the Farnese Hercules or the Diana of Versailles, both based on a Greek sculpture made several centuries earlier. Much of the art found in the remains of Pompeii (including the famously erotic pieces) also demonstrates continuity with earlier Hellenic art.
Whether Roman art is debased Hellenic art, however, is largely a matter of perspective. Hellenic art emphasized the purity and greatness of individuals: look at the Alexander the Great Sculpture of about 320 BCE, showing the famous king with clear face, flowing hair, strong physique, and thoughtful expression. Then look at the famous bust of Scipio, Rome's greatest general: he is bald, the wrinkles on his face show, and his expression is stern. This contrast reflects the Roman artistic desire to express people as they were, rather than how they might want to be idealized. Does this make it "debased"? To the Greek artists, perhaps. No matter your opinion, everyone can agree that the Romans created their own type of art from the inspiration of the Hellenic movement, just as the ancient Carthaginians and Seleucids did, transforming it according to their own customs.