Macedonian Phalanges were extraordinarily slow, and were as inflexible as any of the Greek formations. The tactics of the late Middle Ages, by comparison, are much faster and much more difficult to overcome with a properly disciplined force.
The Roman Empire has as much chance of successfully adopting use of them as the Kingdom of Italy does adopting a European superpower. The Roman nobility that controlled the armies will see muskets as a threat to its political power right up until artillery and musketry smashes the everloving hell out of a legion.
The amusing thing is that the Sassanids or even a Germanic tribe might use gunpowder before the Romans do.