Should I keep my Triarii and Principes?

[econ21]

In TW SP, the real cost of a unit is its upkeep - not its purchase price. That strengthens the argument for getting rid of obsolete units. However, pre-Marian units will do fine against most factions that don't have post-Marian units so maybe shunt them to another front. The economic situation is not usually so tight that you can't afford to retain your pre-Marian army.

But if you are going to fight a powerful Roman faction that also has post-Marian units, you don't want hastati and principes in your frontline stacks. I had a rude shock when I first tried that and was amazed at how outclassed my hitherto unbeatable Romans were when facing even early Roman cohorts.

Triari are ok as superior anti-cav units, but I am not sure spears are that worth it in vanilla RTW. They are rather slow to intercept AI cavalry - you'd be better off using your own heavy cavalry - and if you have to take a cavalry charge, I imagine cohorts would fare about as well as triari (especially if stationary with fire at will on).