Spears are very unbalanced

[Philippus Flavius Homovallumus]

Units that have been kept under arms will have more XP, won't they?

My point is very simple, the base level of training was fairly even and the Romans did not have the elite permenant soldiers other armies did until after Augustus.

So why should a newly recruited Marian cohort be better than a newly recruited unit of mid-level phalangites?

Edit: Just to be very clear here, the post-Marian army was still a militia, conscripted in emergencies, not a proffesional force. Which was why when Pompey returned from the East he had great trouble settling his veterans.