Pikemen

[Litoralis]

The only real use I get out of them is putting a unit in my ports to stop ships raiding them and would never deploy them on the battlefield

I actually sometimes do that with depleted units. Where most of the troops have been killed and you have maybe 20 soldiers. Instead of combining them with other units, retraining them, or disbanding them, put them in ports. It's super cheap upkeep and it keeps the ports from getting raided.