Plumbatarii - Pretty much the same mellee stats as the Comitatenses, but with a better ranged attack. Believe its 2 stronger than the Pila, plus has a range of 70 instead of 45, and finally they carry 14 of them instead of the 3 Pila. Killer infantry unit vs AI.
I suspect that the ERE Plumbatarii would atleast have a chance against them if the immortals are pinned. Javelins are wonderful.