for yeah sure doom a good sorcerour but mephisto rules the underworld and sdoom when he made a deal with demons got his ass wooped and they were weak lower demons so
"Triumph and Tragedy," in which Doom finally got his mother's soul back made a huge deal about how Doom's power was basically a fraction of what he can bring to bear normally- only his sorcery worked, because the laws of physics were under Mephisto's control while in Hell. Dr. Strange has stalemated Mephisto while on Earth using only sorcery, and while this was during Strange's super-badass times, Doom using his science-based abilities as well as his magic is extremely formidable. And Ultimate Doom, while not quite up to 616-Doom-snuff, he's not a joke either.
Mephisto still stomps 'em, but Doom is wily. Two Dooms are twice as wily. They might squeeze a win here or there.